Publications

  1. Comedy YL, Gilbert JE, and Pun SH. Invention is not an option. Technology and Innovation 2017, 18, 267-274.
  2. Cheng YL, Sellers DL, Tan J-KY, Peeler DJ, Horner PJ, and Pun SH. Development of switchable polymers to address the dilemma of stability and cargo release in polycationic nucleic acid carriers. 2017, 127, 89-96.
  3. Lamm RJ, Lim EB, Weigandt KM, Pozzo LD, White NJ, and Pun SH. Peptide valency plays an important role in the activity of a synthetic fibrin-crosslinking polymer. Biomaterials 2017, accepted.
  4. Ngambenjawong C, Pineda JMB, and Pun SH. Engineering an affinity-enhanced peptide through optimization of cyclization chemistry. Bioconj Chem 2016, 77, 2854-2862.
  5. Wu JPJ, Chang B, Roffler SR, Lundy DJ, Yen CYT, Chen P, Lai JJ, Pun SH, Stayton PS, and Hsieh PCH. Reloadable multi-drug capturing drug delivery system for targeted ischemic disease treatment. Sci Trans Med 2016, 8, 365.
  6. Cheng YL, Yumul RC, and Pun SH. Virus-inspired polymer for efficient in vitro and in vivo gene delivery. Angew Chemie 2016, 55, 12013-12017.
  7. Tan JK, Sellers DL, Pam B, Pun SH and Horner PJ. Non-viral nucleic acid delivery strategies to the central nervous system. Frontiers in Mol Neuroscience 2016, 9, 108.
  8. Ngambenjawong C, Gustafson HH, Pineda JM, Cieslewicz ME, and Pun SH. Serum stability and affinity optimization of an M2 macrophage-targeting peptide (M2pep). Theranostics 2016, 6, 1403-1414.
  9. Cheng YL, Wei H, Tan JK, Peeler DJ, Maris DO, Sellers DL, Horner PJ and Pun SH. Nano-sized sunflower polycations as effective gene transfer vehicles. Small 2016, 12, 2750-2758.
  10. Sellers DL, Bergen JM, Johnson RN, Ravits J, Horner PH, and Pun SH. Targeted Axonal Import (TAxI) peptide delivers functional proteins into the spinal cord after peripheral administration. PNAS 2016, 113, 2514-2519.
  11. Chan LW, White NJ, and Pun SH. A novel fibrin-crosslinking polymer to treat coagulopathy of trauma. ACS Biomaterials Sci Eng 2016, 31, 178-185.
  12. Tan JKY, Pham B, Perez C, Zong Y, Hemphill A, Maris DO, Miao C, Matula TJ, Mourad PD, Wei H, Sellers DL, Horner PJ, and Pun SH. Increased intraventricular gene transfer to the brain with a combination of polyplexes, microbubbles, and ultrasound. J. Control. Release 2016, 231, 86-93.
  13. Ngambenjawong C, Cieslewicz M, Schellinger JS, and Pun SH. Synthesis and evaluation of multivalent M2pep peptides for targeting alternatively activated macrophages. J. Control. Release 2016, 224, 103-111.
  14. Jing P, Wu J, Liu GW, Keeler EG, Pun SH, and Lih LY. Photonic crystal optical tweezers with high efficiency for live biological samples and viability characterization. Scientifc Reports 2016, 6, 19924.
  15. Wang CE*, Wei H*, Tan N, Boydston AJ, and Pun SH. Sunflower polymers for folate-mediated drug delivery. Biomacromolecules 2016, 17, 69-75.
  16. Chan LW, Kim CH, Wang X, Pun SH, White NJ, and Kim TH. PolySTAT-modified chitosan gauzes for improved hemostasis in external hemorrhage. Acta Biomaterialia 2016, 31, 178-185.
  17. Wang CE, Stayton PS, Pun SH, and Convertine AJ. Polymer nanostructures synthesized by controlled living polymerization for tumor-targeted drug delivery. J. Control. Release 2015, 219, 345-354.
  18. Wei H*, Wang CE*, Tan N, Boydston AJ, and Pun SH. ATRP synthesis of sunflower polymers using cyclic multimacroinitiators. ACS Macro Lett. 2015, 4, 938-941.
  19. Liu GW*, Livesay BR*, Kacherovsky NA, Cieslewicz M, Waalkes A, Jensen MC, Salipante SJ, and Pun SH. Efficient identification of murine M2 macrophage peptide targeting ligands by phage display and next-generation sequencing. Bioconjugate Chem. 2015, 26, 1811-1817.
  20. Chan LWG, White NJ, and Pun SH. Synthetic strategies for engineering intravenous hemostats. Bioconjugate Chem. 2015, 26, 1224-1236.
  21. Rohani MG, McMahan RS, Razumova MV, Hertz AL, Cieslewicz ME, Pun SH, Regnier M, Wang Y, Birkland TP, and Parks WC. MMP-10 regulates collagenolytic activity of alternatively activated resident macrophages. J. Invest. Derm. 2015, accepted.
  22. Elias PZ, Liu GW, Wei H, Jensen MC, Horner PJ, and Pun SH. A functionalized, injectable hydrogel for localized drug delivery with tunable thermosensitivity: synthesis and characterization of physical and toxicological properties. J. Control. Release 2015, 208, 76-84.
  23. Choi JL*, Tan JKY*, Sellers DL, Wei H, Horner PJ, and Pun SH. Guanidinylated block copolymers for gene transfer: A comparison with amine-based materials for in vitro and in vivo gene transfer efficiency. Biomaterials 2015, 54, 87-96.
  24. Cheng J and Pun SH. Polymeric biomaterials for cancer nanotechnology. Biomaterials Science 2015, 3, 891-893.
  25. Chan LWG, Wang X, Wei H, Pozzo LD, White NJ, and Pun SH. Fibrin-crosslinking polymers for modulating clot properties and inducing hemostasis. Sci. Transl. Med. 2015, 7, 277ra29. (full text)
  26. Chu DSH, Bocek MJ, Shi J, Ta A, Ngambenjawong C, Rostomily RC, and Pun SH. Multivalent display of pendant pro-apoptotic peptides increases cytotoxic activity. J. Control. Release 2015, 205, 155-161.
  27. Wei H and Pun SH. Functional biomaterials synthesized by double-head polymerization agents. Material Matters 2015, 10, 11-14.
  28. Kacherovsky N, Liu GW, Jensen MC, and Pun SH. Multiplexed gene transfer to a human T-cell line by combining Sleeping Beauty transposon system with methotrexate selection. Biotechnol. Bioeng. 2015, 112, 1429-1436.
  29. Tan JKY, Choi JL, Wei H, Schellinger JG, and Pun SH. Reducible, dibromomaleimide-linked polymers for gene delivery. Biomaterials Science 2015, 3, 112-120.
  30. Chu DSH, Sellers DL, Bocek MJ, Fishedick AE, Horner PJ, and Pun SH. MMP-sensitive polymers mediate environmentally-responsive bivalirudin release and thrombin inhibition. Biomaterials Science 2015, 3, 41-45.
  31. Sellers DL, Kim TH, Mount CW, Pun SH, and Horner PJ. Prolonged hirudin delivery from poly(lactic-co-glycolic) acid microspheres encapsulated in Pluronic F-127 and functional recovery from a demyelination lesion. Biomaterials 2014, 35, 8895-8902.
  32. Shi J, Choi JL, Chou B, Johnson RN, Schellinger JG, and Pun SH. Effect of polyplex morphology on cellular uptake, intracellular trafficking, and transgene expression. ACS Nano 2013, 7, 10612-10620.
  33. Shi J, Schellinger JG, and Pun SH. Engineering biodegradable and multifunctional peptide-based polymers for gene delivery. J. Biol. Eng. 2013, 7, 25.
  34. Wei H*, Chu DSH*, Zhao J, Pahang J, and Pun SH. Synthesis and evaluation of cyclic cationic polymers for gene delivery. ACS Macro Lett. 2013, 2, 1047-1050.
  35. Cieslewicz M, Tang J, Yu JL, Cao H, Zavaljevski M, Motoyama K, Lieber A, Raines EW, and Pun SH. Targeted delivery of proapoptotic peptides to tumor-associated macrophages improves survival. PNAS 2013, 110, 15919-15924.
  36. Tsui JH, Lee W, Pun SH, Kim J, and Kim DH. Microfluidics-assisted in vitro drug screening and carrier production. Adv. Drug Del. Rev. 2013, 65, 1575-1588.
  37. Burke P, Pun SH, and Reineke TM. Advancing polymeric delivery systems amidst a nucleic acid therapy renaissance. ACS Macro Lett. 2013, 2, 928-934.
  38. Schellinger JG, Pahang JA, Shi J, and Pun SH. Block copolymers containing a hydrophobic domain of membrane-lytic peptides form micellar structures and are effective gene delivery agents. ACS Macro Lett. 2013, 2, 725-730.
  39. Chu DSH, Schellinger JG, Bocek MJ, Johnson RN, and Pun SH. Optimization of Tet1 ligand density in HPMA-co-oligolysine copolymers for targeted neuronal gene delivery. Biomaterials 2013, 34, 9632-9637.
  40. Wei H, Volpatti LR, Sellers DL, Maris DO, Andrews IW, Hemphill AS, Chan LW, Chu DS, Horner PJ, and Pun SH. Dual-responsive, stabilized nanoparticles for efficient in vivo plasmid delivery. Angew. Chem. Int. Ed. Engl. 2013, 52, 5377-5381. *Selected as Very Important Paper (VIP)
  41. Shi J, Schellinger JG, Johnson RN, Choi JL, Chou B, Anghel EL, and Pun SH. Influence of histidine incorporation on buffer capacity and gene transfection efficiency of HPMA-co-oligolysine brush polymers. Biomacromolecules 2013, 14, 1961-1970.
  42. Carlson PM, Schellinger JG, Pahang JA, Johnson RN, and Pun SH. Comparative study of guanidine-based and lysine-based brush copolymers for plasmid delivery. Biomater. Sci. 2013, 1, 736-744.
  43. Shi J, Chou B, Choi JL, Ta AL, and Pun SH. Investigation of polyethylenimine/DNA polyplex transfection to cultured cells using radiolabeling and subcellular fractionation methods. Mol. Pharm. 2013, 10, 2145-2156.
  44. Zhang L, Sinclair A, Cao Z, Ella-Menye J-R, Xu X, Carr L, Pun SH, and Jiang S. Hydrolytic cationic ester microparticles for highly efficient DNA vaccine delivery. Small 2013, 9, 3439-3444.
  45. Chen C-Y, Kim TH, Wu W-C, Huang CM, Wei H, Mount CW, Tian Y, Jang S-H, Pun SH, and Jen AK-Y. pH-dependent, thermosensitive polymeric nanocarriers for drug delivery to solid tumors. Biomaterials 2013, 34, 4501-4509.
  46. Chan LW, Wang Y-N, Lin LY, Upton MP, Hwang JH, and Pun SH. Synthesis and characterization of anti-EGFR fluorescent nanoparticles for optical molecular imaging. Bioconjugate Chem. 2013, 24, 167-175.
  47. Wei H, Pahang JA, and Pun SH. Optimization of brush-like cationic copolymers for non-viral gene delivery. Biomacromolecules 2012, 14, 275-284.
  48. Schellinger JG, Pahang JA, Johnson RN, Chu DSH, Sellers DL, Maris DO, Convertine AJ, Stayton PS, Horner PJ, and Pun SH. Melittin-grafted HPMA-oligolysine based copolymers for improved gene delivery. Biomaterials 2012, 34, 2318-2326.
  49. Berguig GY, Convertine AJ, Shi J, Palanca-Wessels MC, Duvall CL, Pun SH, Press OW, and Stayton PS. Intracellular delivery and trafficking dynamics of a lymphoma-targeting antibody-polymer conjugate. Mol. Pharm. 2012, 9, 3506-3514.
  50. Wei H, Schellinger JG, Chu DSH, and Pun SH. Neuron-targeted copolymers with sheddable shielding blocks synthesized using a reducible, RAFT-ATRP double-head agent. J. Am. Chem. Soc. 2012, 134, 16554-16557.
  51. Kacherovsky N, Harkey MA, Blau CA, Giachelli CM, and Pun SH. Combination of Sleeping Beauty transposition and Chemically Induced Dimerization selection for robust production of engineered cells. Nucleic Acids Res. 2012, 40, e85.
  52. Chu DSH, Schellinger JG, Shi J, Convertine AJ, Stayton PS, and Pun SH. Application of controlled radical polymerization for nucleic acid delivery. Acc. Chem. Res. 2012, 45, 1089-1099.
  53. Chu DSH, Johnson RN, and Pun SH. Cathepsin B-sensitive polymers for compartment-specific degradation and nucleic acid release. J. Control. Release 2012, 157, 445-454.
  54. Shi J*, Johnson RN*, Schellinger JG, Carlson PM, and Pun SH. Reducible HPMA-co-oligolysine copolymers for nucleic acid delivery. Int. J. Pharm. 2012, 427, 113-122.
  55. Kim TH, Mount CW, Dulken BW, Ramos J, Fu CJ, Khant HA, Chiu W, Gombotz W, and Pun SH. Filamentous, mixed micelles of triblock copolymers enhance tumor localization of indocyanine green in a murine xenograft model. Mol. Pharm. 2012, 9, 135-143.
  56. Wang CH, Chan LW, Johnson RN, Chu DSH, Shi J, Schellinger JG, Lieber A, and Pun SH. HPMA-co-oligolysine copolymer-coated adenovirus transduce CAR-negative cells through interaction with sulfate proteoglycans. Biomaterials 2011, 3, 9536-9545.
  57. Johnson RN, Chu DSH, Shi J, Schellinger JG, Carlson PM, and Pun SH. HPMA-oligolysine copolymers for gene delivery: optimization of peptide length and polymer molecular weight. J. Control. Release 2011, 15, 303-311.
  58. Kim YS, Park IK, Kim WJ, Yu MK, Jon S, Pun SH, Jeong MH, and Ahn Y. SPION nanoparticles as efficient probe and carrier of DNA to umbilical cord blood-derived mesenchymal stem cells. J. Nanosci. Nanotech. 2011, 1, 1507-1510.
  59. Wang CH and Pun SH. Substrate-mediated nucleic acid delivery from self-assembled monolayers. Trends Biotechnol. 2011, 29, 119-126.
  60. Johnson RN, Burke RS, Convertine A, Hoffman AS, Stayton PS, and Pun SH. Synthesis of statistical copolymers with multiple functional peptides via RAFT polymerization. Biomacromolecules 2010, 11, 3007-3013.
  61. Wang CH, Jiang S, and Pun SH. Localized cell uptake of His-tagged polyplexes immobilized on NTA self-assembled monolayers. Langmuir 2010, 26, 15445-15452.
  62. Kim TH, Mount CW, Gombotz WR, and Pun SH. The delivery of doxorubicin to 3-D multicellular spheroids and tumors in a murine xenograft model using tumor-penetrating triblock polymeric micelles. Biomaterials 2010, 31, 7386-7397.
  63. Kim TH, Chen YP, Mount CW Gombotz WR, Li XD, and Pun SH. Evaluation of temperature-sensitive, indocyanine green-encapsulating micelles for noninvasive near-infrared tumor imaging. Pharm. Res. 2010, 27, 1900-1913.
  64. Wilson BK, Mentele T, Bachar S, Knouf E, Bendoraite A, Tewari M, Pun SH, and Lin LY. Nanostructure-enhanced laser tweezers for efficient trapping and alignment of particles. Opt. Express 2010, 18, 16005-16013.
  65. Kwon EJ, Liong S, and Pun SH. A truncated HGP peptide sequence retains endosomolytic activity and improves gene delivery efficiencies. Mol. Pharm. 2010, 7, 1260-1265.
  66. Kwon EJ, Lasiene J, Jacobson B, Park IK, Horner PJ, and Pun SH. Targeted nonviral delivery vehicles to neural progenitor cells in the mouse subventricular zone. Biomaterials 2010, 31, 2417-2424.
  67. Burke RS and Pun SH. Synthesis and characterization of biodegradable HPMA-oligolysine copolymers for improved gene delivery. Bioconjugate Chem. 2010, 2, 140-150.
  68. Miao X, Wilson BK, Cao G, Pun SH, and Lin LY. Long-range trapping and rotation of nanowires and nanotubes by plasmonic tweezers. IEEE Journal of Selected Topics in Quantum Electronics 2009, 15, 1515-1520.
  69. Kwon JS, Park IK, Cho AS, Shin SM, Hong MH, Jeong SY, Kim YS, Min JJ, Kim WJ, Jo S, Pun SH, Cho JG, Park JC, Kang JC, and Ahn Y. Enhanced angiogenesis mediated by vascular endothelial growth factor plasmid-loaded thermo-responsive amphiphilic polymer in a rat myocardial infarction model. J. Control. Release 2009, 138, 168-176.
  70. Ng CP, Goodman TT, Park IK, and Pun SH. Bio-mimetic surface engineering of plasmid-loaded nanoparticles for active intracellular trafficking by actin comet-tail motility. Biomaterials 2009, 30, 951-958.
  71. Miao X, Wilson BK, Pun SH, and Lin LY. Optical manipulation of micron/submicron particles and biomolecules through plasmonics. Opt. Express 2008, 16, 13517-13525.
  72. Goodman TT, Ng CP, and Pun SH. 3-D tissue culture systems for the evaluation and optimization of nanoparticle-based drug carriers. Bioconjugate Chem. 2008, 19, 1951-1959.
  73. Kwon EJ, Bergen JM, Park IK, and Pun SH. Peptide-modified vectors for nucleic acid delivery to neurons. J. Control. Release 2008, 132, 230-235.
  74. Goodman TT, Chen J, Matveev K, and Pun SH. Spatio-temporal modeling of nanoparticle delivery to multicellular spheroids. Biotechnol. Bioeng. 2008, 101, 388-399.
  75. Kwon EJ, Bergen JM, and Pun SH. Application of an HIV gp41-derived peptide for enhanced intracellular trafficking of synthetic gene and siRNA delivery vehicles. Bioconjugate Chem. 2008, 19, 920-927.
  76. Burke RS and Pun SH. Extracellular barriers to in vivo PEI and PEGylated PEI polyplex-mediated gene delivery to liver. Bioconjugate Chem. 2008, 19, 693-704.
  77. Park IK, Ng CP, Wang J, Chu BC, Wang C, and Pun SH. Determination of nanoparticle vehicle unpackaging by MR imaging of a T(2) magnetic relaxation switch. Biomaterials 2008, 29, 724-732.
  78. Ng CP and Pun SH. A perfusable 3D cell-matrix tissue culture chamber for in situ evaluation of nanoparticle vehicle penetration and transport. Biotechnol. Bioeng. 2008, 99, 1490-1501.
  79. Bergen JM, Kwon EJ, Shen TW, and Pun SH. Application of an environmentally sensitive fluorophore for rapid analysis of the binding and internalization of gene carriers. Bioconjugate Chem. 2008, 19, 377-384.
  80. Bergen JM and Pun SH. Analysis of the intracellular barriers encountered by nonviral gene carriers in a model of spatially controlled delivery to neurons. J. Gene Med. 2008, 10, 187-197.
  81. Saul JM, Wang CK, Ng CP, and Pun SH. Multilayer nanocomplexes of polymer and DNA exhibit enhanced gene delivery. Adv. Mater. 2008, 20, 19-25.
  82. Bergen JM, Park IK, Horner PJ, and Pun SH. Nonviral approaches for neuronal delivery of nucleic acids. Pharm. Res. 2008, 25, 983-998.
  83. Rodriguez VB, Henry SM, Hoffman AS, Stayton PS, Li X, and Pun SH. Encapsulation and stabilization of indocyanine green within poly(styrene-alt-maleic anhydride) block-poly(styrene) micelles for near-infrared imaging. J. Biomed. Opt. 2008, 13, 014025.
  84. Park IK, Lasiene J, Chou SH, Horner PJ, and Pun SH. Neuron-specific delivery of nucleic acids mediated by Tet1-modified poly(ethylenimine). J. Gene Med. 2007, 9, 691-702.
  85. Saul JM, Linnes MP, Ratner BD, Giachelli CM, and Pun SH. Delivery of non-viral gene carriers from sphere-templated fibrin scaffolds for sustained transgene expression. Biomaterials 2007, 28, 4705-4716.
  86. Housni A, Cai H, Liu S, Pun SH, and Narain R. Facile preparation of glyconanoparticles and their bioconjugation to streptavidin. Langmuir 2007, 23, 5056-5061.
  87. Goodman TT, Olive PL, and Pun SH. Increased nanoparticle penetration in collagenase-treated multicellular spheroids. Int. J. Nanomedicine 2007, 2, 265-274.
  88. Bergen JM and Pun SH. Evaluation of an LC8-binding peptide for the attachment of artificial cargo to dynein. Mol. Pharm. 2007, 4, 119-128.
  89. Cheng J, Zeidan R, Mishra S, Liu A, Pun SH, Kulkarni RP, Jensen GS, Bellocq NC, and Davis ME. Structure-function correlation of chloroquine and analogues as transgene expression enhancers in nonviral gene delivery. J. Med. Chem. 2006, 49, 6522-6531.
  90. Park IK, von Recum HA, Jiang S, and Pun SH. Supramolecular assembly of cyclodextrin-based nanoparticles on solid sufaces for gene delivery. Langmuir 2006, 22, 8478-8484.
  91. Bergen JM, von Recum HA, Goodman TT, Massey AP, and Pun SH. Gold nanoparticles as a versatile platform for optimizing physicochemical parameters for targeted drug delivery. Macromol. Biosci. 2006, 6, 506-516.
  92. Popielarski SR, Pun SH, and Davis ME. A nanoparticle-based model delivery system to guide the rational design of gene delivery to the liver 1 Synthesis and characterization. Bioconjugate Chem. 2005, 16, 1063-1070.
  93. Bergen JM and Pun SH. Peptide-enhanced gene delivery. MRS Bulletin 2005, 3, 663-667.
  94. Pack DW, Hoffman AS, Pun SH, and Stayton PS. Design and development of polymers for gene delivery. Nat. Rev. Drug Discov. 2005, 4, 581-593.
  95. Bellocq NC, Kang DW, Wang X, Jensen GS, Pun SH, Schleup T, Zepeda ML, and Davis ME. Synthetic biocompatible cyclodextrin-based constructs for local gene delivery to improve cutaneous wound healing. Bioconjugate Chem. 2004, 15, 1201-1211.
  96. Pun SH, Bellocq NC, Liu A, Jensen G, Machemer T, Quijano E, Schluep T, Wen S, Engler H, Heidel J, and Davis ME. Cyclodextrin-modified polyethylenimine polymers for gene delivery Bioconjugate Chem. 2004, 15, 831-840.
  97. Pun SH and Davis ME. Cyclodextrin polymers for gene delivery. Chapter in Polymeric Gene Delivery. 2004, CRC Press, Mansoor Amiji, Ed.
  98. Pun SH, Tack F, Bellocq NC, Cheng J, Grubbs BH, Jensen GS, Davis ME, Brewster M, Janicot M, Janssens B, Floren W, and Bakker A. Targeted delivery of RNA-cleaving DNA enzyme (DNAzyme) to tumor tissue by transferrin-modified, cyclodextrin-based particles. Cancer Biol. Ther. 2004, 3, 641-650.
  99. Davis ME, Pun SH, Bellocq NC, Reineke TM, Popielarski SR, Mishra S, and Heidel JD. Self-assembling nucleic acid delivery vehicles via linear, water-soluble, cyclodextrin-containing polymers. Curr. Med. Chem. 2004, 11, 179-197.
  100. Bellocq NC, Pun SH, Jensen GS and Davis ME. Transferrin-containing, cyclodextrin polymer-based particles for tumor-targeted gene delivery. Bioconjugate Chem. 2003, 14, 1122-1132.
  101. Pun SH and Davis ME. Development of a nonviral gene delivery vehicle for systemic application Bioconjugate Chem. 2002, 13, 630-639.
  102. Hwang SJ and Davis ME. Cationic polymers for gene delivery: designs for overcoming barriers to systemic administration. Curr. Opin. Mol. Ther. 2001, 3, 183-191.
  103. Bellocq NC, Hwang SJ, and Davis ME. Optimization of cyclodextrin-polymers specifically designed for gene delivery. Proceedings of the 221st American Chemical Society National Meeting, Polymeric Materials: Science & Engineering 2001, 8, 809-810.
  104. Hwang SJ, Bellocq NC, and Davis ME. Effects of structure of beta-cyclodextrin-containing polymers on gene delivery. Bioconjugate Chem. 2001, 12, 280-290.
  105. Gonzalez H, Hwang SJ, and Davis ME. New class of polymers for the delivery of macromolecular therapeutics. Bioconjugate Chem. 1999, 10, 1068-1074.
  106. McDaniel R, Kao C, Hwang SJ, and Khosla C. Engineered intermodular and intramodular polyketide synthase fusions. Chem. Biol. 1997, 4, 667-674.