The chicken ubiquitin gene contains a heat shock promoter and expresses an unstable mRNA in heat-shocked cells

Abstract

A chicken genomic library was screened to obtain genomic clones for ubiquitin genes. Two genes that differ in their genomic location and organization were identified. One gene, designated Ub I, contains four copies of the protein-coding sequence arranged in tandem, while the second gene, Ub II, contains three. The origin of the two major mRNAs that are induced after heat shock in chicken embryo fibroblasts was determined by generating DNA probes from the 5'-and 3'-noncoding regions of the two genes. Both mRNAs are transcribed from Ub I, the larger being the unspliced precursor of the smaller. A 674-base-pair intron was located within the 5'-noncoding region of Ub I. The second gene, Ub II, does not appear to code for an RNA species in normal or heat-shocked chicken embryo fibroblasts. The expression of ubiquitin mRNA during heat shock and recovery was examined. Addition of actinomycin D before heat shock completely abolished the response of ubiquitin mRNA to the stress. Analysis of the stability of the mRNA during recovery revealed that the mRNA accumulated during the heat shock is rapidly degraded with a half-life of approximately 1.5 h, suggesting a specialized but transient role for ubiquitin during heat shock.