Patrick K. Bender

Two exons encode the calmodulin-binding domain in the mouse phosphorylase kinase catalytic subunit gene☆

The catalytic subunit, gamma, of phosphorylase kinase contains two calmodulin-binding sequences that define a domain in gamma that is homologous to the troponin-C-binding domain in troponin I. The homology is based on both sequence and functional similarities. To account for this homology, it has been proposed that the calmodulin-binding sequences in gamma and the troponin-C-binding domain in troponin I have evolved from a common ancestor. We investigated this possibility by comparing the exon structure of the gamma gene with that of troponin-I gene over their homologous domains. In the quail troponin-I gene, it is known that the entire troponin-C-binding domain is encoded by a single exon. However, two exons are found to encode the calmodulin-binding domain in the gamma gene from mouse. This result indicates that convergent evolution may be responsible for the sequence and functional similarities between the homologous domains in troponin I and gamma.

Phosphorylase kinase activity in I/strain neonatal skeletal muscle with a deficiency in αα′ subunit mRNAs

Abstract In the adult I LnJ mouse skeletal muscle, phosphorylase kinase activity is 0.2% of that in normal. This deficiency results from a paucity of mRNAs for the phosphorylase kinase regulatory subunit- α and its isoform α′. However, in the I LnJ neonatal skeletal muscle phosphorylase kinase activity is 20–25% of that in normal. During the first two months of development this activity decreases while in normal tissue it increases. The developmental differences in the magnitude of the I LnJ deficiency indicate the possibility of stage specific mechanisms regulating the accumulation of α α′ mRNAs. To investigate this possibility, the abundance of α α′ mRNAs and of the catalytic subunit, γ, mRNAs were compared by Northern Blot analysis. The results demonstrate that neonatal and adult I LnJ skeletal muscle have a similar paucity of α α′ mRNAs whereas accumulation of γ mRNAs is not significantly different from normal.