Cyclic-AMP-dependent protein kinase and a transmembrane tyrosine phosphatase in Caenorhabditis elegans: Structure, function and regulation

Abstract

Protein kinases and protein phosphatases are central components of signal transduction pathways. This thesis characterized two important proteins involved in signaling in C. elegans, the regulatory subunit (R) of cAMP-dependent protein kinase (cAMP-PK) and a tyrosine phosphatase (PTPase).;C. elegans has a single gene and mRNA encoding the R subunit of cAMP-PK of 376 amino acid residues. The highest overall sequence identity is 55% as compared with a mammalian RI isoform. The C-terminal region (residues 146-376) which includes two cAMP-binding sites, is more conserved (69% identity). However, C. elegans R has a unique N-terminal region (residues 45-145). Novel sequences in this segment of the polypeptide may confer functional properties that are served by four separate R isoforms in mammals. This notion is supported by the fact that approximately 60% of the cAMP-binding and kinase activities were bound to particulate structures. Immunocytochemistry showed that particulate R was predominantly enriched in the pharyngeal nerve ring.;Expression of catalytic (C) and R subunits was low in embryos. The abundance of C and R increased prior to hatching and was elevated 10-fold as the worms emerged from the eggs. Similar amounts of C and R were observed at later developmental stages. However, the C and R mRNA content varied minimally during development suggesting that the expression is controlled post-transcriptionally.;A 4.67kb cDNA for a C. elegans PTPase has been cloned. It predicts a polypeptide with 623 extracellular residues, 23-residue transmembrane segment and 680-residue C-terminal cytoplasmic region that is followed by a translation stop codon. The C-terminal 577 residues are 55% identical with the PTPase catalytic domains of the human LAR (leucocyte common antigen related protein). N-terminal residues 1 to 110 are 28% identical to fibronectin type III repeat (FN III). The remaining residues connecting the FN III and the catalytic domain are not related to other proteins in various data bases. The cDNA detects 5 kb mRNA. The PTPase gene has been mapped to chromosome II (R) and is positioned between Unc-4 and Sqt-1.