S-(beta-Aminoethyl)-cysteine (AEC) resistance was achieved in Corynebacterium glutamicum by cloning a chromosomal 1.5-kb EcoRV-BglII DNA fragment on a multicopy plasmid. DNA sequence analysis of the 1.5-kb DNA fragment revealed an open reading frame (ORF326) which represents the AEC resistance gene, designated aecD. The aecD gene directs the synthesis of a 36-kDa protein which was visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The aecD gene is a nonessential gene and mediates AEC resistance only in an amplified state. C. glutamicum strains harboring an amplified aecD gene can utilize AEC as an alternative nitrogen source, indicating that the AEC resistance mechanism is due to AEC degradation. Since the AEC degradation products analyzed by high-pressure liquid chromatography were found to be pyruvate and aminoethanethiol (cysteamine), it was concluded that the aecD gene encodes a C-S lyase with alpha, beta-elimination activity. Besides AEC, the C-S lyase was also able to use cysteine, cystine, and cystathionine as substrates.

Run-off transcription in nuclei isolated from soybean seedlings was used to test the hypothesis Ihat the expression of heat shock genes is controlled at the level of transcription. Only nuclei pretreated by a heat shock at 41 °C prior to their isolation synthesized RNA from heat shock genes. The specificity of transcripts was determined by Southern blot hybridization of [^"^P]-labelled run-off RNA with DNA fragments from several heat shock and non-heat shock genes. The strand selectivity of heat shock gene transcription was exemplified by single stranded DNA probes. Low concentrations of a-amanitin completely inhibited the synthesis of heat shock specific RNA, but only partially inhibited the synthesis of ribosomal RNA. The overall transcription of nuclei isolated from heat shock tissue was reduced by more than 20% compared to that in nuclei from control tissue. This decline is consistent with a decrease in the transcriptional activity of nonheat shock genes transcribed by RNA polymerases I and H. Our results suggest that temperature stress induces the transcriptional activation of heat shock genes and has a negative effect on the transcription of other genes.

No abstract