A B2 repeat insertion generates alternate structures of the mouse muscle gamma-phosphorylase kinase gene

A variety of cDNA and genomic clones for the gamma-subunit of mouse muscle phosphorylase kinase (Phk-gamma M) have been isolated and characterized. The murine gene for Phk-gamma M (Phkg) exhibits multiple transcription start sites that are identical in skeletal muscle, cardiac muscle, and brain. The gene is composed of 10 exons and includes a 4.9-kb intron located in the 5' untranslated region. Two mRNA species of 1.75 and 2.55 kb are produced from Phkg in ICR and C57BL/10 mice; these transcripts are colinear throughout the coding region and differ only in the length of the 3' untranslated region. We have mapped the polyadenylation site of the 1.75-kb mRNA to the middle of exon 10; the 2.55-kb mRNA terminates further 3' at the end of a mouse B2 repeat. In Balb/C mice an additional B2 insertion and related genomic rearrangements alter the sequence of Phkg exon 10 and are accompanied by an increase in the quantity of the 1.75-kb transcript and a decrease in the abundance and size of the longer transcript, from 2.55 to 2.35 kb. A PCR assay for sequences contained in exon 10 reveals that the Balb/C 3' gene structure is shared by Mus musculus castaneus and Mus musculus molossinus; the C57BL/10 gene structure is shared by Mus spretus, Mus domesticus, and several strains of laboratory mice. These results suggest that Phkg in Balb/C mice was derived from M. m. molossinus and that Phkg of the other examined laboratory strains was derived from M. domesticus.