EXTENSIVE ALTERNATE EXON USAGE AT THE 5'-END OF THE SHEEP TROPOELASTIN GENE

Several overlapping cDNA clones were isolated from a lambda gtl0 cDNA library constructed using polyA+ RNA from neonatal sheep lung. DNA seq uence analysis of these cDNA recombinants revealed the complete derive d amino acid sequence of sheep tropoelastin. A comparison of DNA seque nces from individual sheep tropoelastin cDNA also confirmed the presen ce of several tropoelastin mRNA isoforms in neonatal lung tissue. Codi ng domains corresponding to exons 13, 14 and 33 were present in severa l of the sheep tropoelastin cDNA fragments but absent in others. The r elative amount of alternate usage of these exons was quantitated by po lymerase chain amplification. In confirmation of previous studies in o ther mammalian species, extensive alternate usage of exon 33 was obser ved in total RNA isolated from aorta, nuchal ligament and pulmonary ar tery from neonatal sheep. In striking contrast to all previous studies , however, exons 13 and 14 were shown to be subject to almost the same level of alternate usage as exon 33 in all three neonatal sheep tissu es examined.