Characterization and expression of the mouse Hsc70 gene

A genomic clone encoding the mouse Hsc70 gene has been isolated and characterized by DNA sequence analysis. The gene is approximately 3.9 kb in length and contains eight introns, the fifth, sixth and eighth of which encode the three U14 snoRNAs. The gene has been located on Chr 9 in the order FliI-Itm1-Olfr7-Hsc70(Rnu14)-Cbl by genetic analysis. Expression of Hsc70 is universal in all tissues of the mouse, but is slightly elevated in liver, skeletal muscle and kidney tissue, while being depressed in testes. In cultured mouse NIH 3T3 cells or human HeLa cells, Hsc70 mRNA levels are low under normal conditions, but can be induced 8-fold higher in both lines by treatment with the amino acid analog azetidine. A similar induction is seen in cells treated with the proteosome inhibitor MG132 suggesting that elevated Hsc70 expression may be coupled to protein degradation. Surprisingly, expression of the human Hsc70 gene is also regulated by cell-cycle position being 8-10-fold higher in late G₁/S-phase cells as opposed to the levels in early G₁-phase cells.