Abstract. The calcium ionophore A23187 can reversibly induce the expression of two glucose-regulated genes, p3C5 and p4A3. This induction requires a continuous presence of the ionophore for over 2 h. Although extracellular Ca 2+ is important for the optimal effect of A23187, it is not necessary for the induction, since a similar response with a lower magnitude can be triggered in cells cultured in low Ca 2+ medium buffered with EGTA. Both the basal and induced levels of p3C5 and p4A3 transcripts can be modulated by the calmodulin antagonist W-7, indicating the involvement of CaE+/calmodulin-associated pathways. In addition, the sensitivity of the A23187 induction to cycloheximide suggests that the induction process is dependent on de novo protein synthesis.

Recently, a ( subunit for the rat gastric H+,K+-ATPase (HK(), which is structurally similar to the 13 subunit of Na+,K+-ATPase, has been cloned and character-

The properties of two Chinese hamster temperature-sensitive mutants, K12 and H3.5, were examined. Both mutants originated from the same parental cell line, Wg1A, and were isolated as cell cycle mutants arrested in G1. Previously, we had been shown that the H3.5 ts mutation affected the transfer of the oligosaccharide from the lipid carrier to the nascent polypeptide and that the K12 ts mutation regulated the transcription of two glucose/calcium-regulated genes. We report here that these two mutants exhibit almost identical phenotypes at the biochemical level. Furthermore, a genetic complementation test demonstrates that the two ts lesions must be closely related, or even identical. Our results suggest that a specific defect in glycosylation may result in the overproduction of the glucose/calcium-regulated proteins and is capable of activating the promoter of the major glucose-regulated gene.

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