TISSUE-SPECIFIC ALTERNATIVE PROMOTERS REGULATE THE EXPRESSION OF THE 2 SARCO ENDOPLASMIC-RETICULUM CA-ATPASE ISOFORMS FROM ARTEMIA-FRANCISCANA

The sarco/endoplasmic reticulum Ca-ATPase gene from Artemia franciscan a is transcribed into two mRNAs of 4.5 and 5.2 kb that code for protei n isoforms differing at their carboxyl terminus, Northern blot assays and anchored polymerase chain reaction (PCR) experiments have shown th at these two mRNAs also differ at the initial part of their 5' untrans lated region. The 5.2-kb mRNA-specific 5' untranslated region is prese nt as an independent exon whose transcription is regulated by a promot er different from the one previously described that regulates the expr ession of the 4,5-kb mRNA. The nucleotide sequence of the Sd-kb mRNA p romoter and the transcription initiation site have been determined. Th ese results suggest that the expression of the two protein isoforms is regulated in A, franciscana at the transcription initiation step, in contrast with the vertebrates sarco/endoplasmic reticulum Ca-ATPase ge nes 1 and 2 which have unique promoters for transcription of the two i soforms encoded by each gene.