Molecular cloning of a unique complementary DNA of rat myosin regulatory light chain and its elevated expression in v-src-transformed rat culture cell lines.

We have isolated a complementary DNA (cDNA) clone, termed N14, from a cDNA library derived from normal rat fibroblast 3Y1 cells using a differential screening procedure. N14 cDNA was 1115 nucleotides in length and contained an open reading frame of 172 amino acid residues. The expression of N14 gene was significantly increased in Rous sarcoma virus-transformed 3Y1 cells (SR-3Y1) compared with that in parental 3Y1 cells. The high level of N14 gene expression was reduced by treatment with herbimycin A, indicating that the expression was dependent upon the activity of pp60v-src tyrosine kinase. A homology search revealed that the nucleotide sequence of N14 cDNA was nearly identical to that of the rat nonsarcomeric myosin regulatory light chain cDNA (RLC-B), with the exception of a 250-nucleotide insertion which is present between C at position +483 and G at position +484 in the RLC-B cDNA. Southern blot analysis indicated that N14 gene was present as a single copy in the rat genome. Therefore, these two mRNAs might be generated through the alternative splicing mechanism. However, a RNase protection assay revealed that RLC-B mRNA was not expressed in SR-3Y1 cells. In addition, the amount of N14 mRNA was also increased in other types of transformed cells, including v-mos-, simian virus 40-, and v-Ha-ras-transformed 3Y1 cells.