Developmental variations in the splicing pattern of transcripts from the Drosophila gene encoding myosin alkali light chain result in different carboxyl-terminal amino acid sequences.

The total sequence of the Drosophila melanogaster gene encoding the myosin light chain dissociated by alkali (MLC-ALK) has been determined. By sequence comparisons with an MLC-ALK cDNA clone and by S1 nuclease analyses, the pattern of introns and exons within the gene has been deduced. There are multiple polyadenylylation signals that can account for most of the observed heterogeneity in the lengths of mRNAs. In the 3' half of the gene, there are two alternative splicing patterns which result in mRNAs that translate to give proteins with two alternative 14 amino acid carboxyl-terminal sequences. There is developmental regulation of the selection of the above splicing sites. One splicing pattern produces an mRNA that translates into a protein used for both larval and adult musculature, whereas the other splicing pattern is used for the latter stage only.