CHARACTERIZATION OF AN INTRON SPLICE ENHANCER THAT REGULATES ALTERNATIVE SPLICING OF HUMAN GH PRE-MESSENGER-RNA

Splicing of pre-mRNA transcripts is regulated by consensus sequences a t intron (intervening sequence, IVS) boundaries and the branch site, P n vitro studies have shown that the small introns of some genes also r equire intron splice enhancers (ISE) to modulate splice site selection , An autosomal dominant form of isolated GH deficiency (IGHD-II) is ca used by mutations in IVS3 of the GH-1 gene that cause exon 3 (E3) skip ping, resulting in truncated hGH products that prevent secretion of no rmal hGH, Interestingly, some of these IGHD-II mutations perturb an IS E that is buried in IVS3, We localized this ISE by quantitating the ef fects of deletions within IVS3 on E3 skipping. The importance of indiv idual nucleotides to ISE function was determined by analyzing the effe cts of point mutants and additional deletions. Our results show that ( i) an ISE with a G(2)X(1-4)G(3) motif resides in IVS3 of GH-1; (ii) bo th runs of Gs are required for ISE function; (iii) a single copy of th e ISE regulates E3 skipping and (iv) ISE function can be modified by a n adjacent AC element. Our findings reveal a new mechanism by which mu tations can cause inherited human endocrine disorders and suggest that (i) ISEs may regulate splicing of transcripts of other genes and (ii) mutations of these ISEs or of the trans-acting factors that bind them may cause other genetic disorders.