cDNA cloning of a chick homologue of human ATPase complex subunit 4, quantitative tissue distribution and tertiary structure comparison of the ATPase domain to RecA.
The ocular lens consists of a single layer of epithelial cells on its anterior surface and underlying fiber cells, which are derived from the epithelial cells by differentiation and make up the bulk of the lens. Because lens cells are segregated by age and stage of differentiation, we are using this tissue to study the role of the proteasome in differentiation. The purpose of this study is to corroborate the ATPase function of chick subunit 4 (cS4) and assess the levels of the mRNA in the differentiating lens relative to other tissues. We have generated a computer model of the tertiary structure of the ATPase domain of the cS4 of the ATPase complex that regulates the 20S proteasome. The predicted polypeptide from the cloned cDNA of cS4 (440 residues) had a calculated molecular mass of 49,182 and is 98 and 73% identical to human and yeast S4 protein sequences, respectively. A computer search for comparison with known proteins in GenBank showed that the cS4 protein sequence has a conserved region of about 200 amino acid residues including an ATP/GTP binding site and a mitochondrial energy transfer proteins signature sequence. Based on secondary structure, the computer-generated model of the ATPase domain is comparable to that of RecA, with a root mean square deviation of 0.851 from the RecA triad. mRNA in the 14-day-old chick embryo lens is derived primarily (90%) from differentiating cells. The level of cS4 mRNA determined by quantitative RT/PCR in this differentiating tissue was comparable to the cS4 mRNA levels in chick liver, heart, and brain.
Singh
I
I
Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark 07103, USA.
Cai
H
H
Wagner
B J
BJ
D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D002642:Chick Embryo; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics*; D006801:Humans; D007908:Lens, Crystalline / Q000166:cytology / Q000201:enzymology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011938:Rec A Recombinases / Q000737:chemistry* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014018:Tissue Distribution
D018076:DNA, Complementary; D012333:RNA, Messenger; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases