I/Lyn mouse phosphorylase kinase deficiency: mutation disrupts expression of the alpha/alpha'-subunit mRNAs.

A cDNA encoding the alpha subunit of mouse skeletal muscle phosphorylase kinase was used to compare the expression of alpha mRNAs in normal and phosphorylase kinase-deficient tissues of the I/Lyn mouse. The results demonstrate that two different molecular weight species of poly(A)+ RNA in normal mouse heart and skeletal muscle hybridize to the alpha cDNA. These two mRNAs direct the synthesis of alpha protein and its isoform alpha' in a cell-free translation system. Thus, alpha and alpha' are encoded by two distinct mRNAs. The abundance of both of these mRNAs is reduced dramatically in the phosphorylase kinase-deficient skeletal muscle and heart tissues from the I/Lyn mouse strain. This result indicates that a mechanism common to both alpha and alpha' expression is disrupted by the I/Lyn mutation. The I/Lyn deficiency is inherited as an X chromosome trait. By Southern mapping of Chinese hamster-mouse cell hybrids the alpha gene was localized to the mouse X chromosome, supporting the possibility that the I/Lyn mutation is in the alpha gene. These results are discussed in terms of a cis or trans mutation influencing the expression of either a single alpha/alpha' gene or two genes encoding alpha and alpha'.