1887

Abstract

Ribonucleotide reductases (RNRs) are a family of complex enzymes that play an essential role in all organisms because they catalyse synthesis of deoxyribonucleotides required for DNA replication and repair. Three different classes of RNR have been described according to their metal cofactors and organic radicals. Class Ib RNR is encoded in four different genes (, , and ) organized in an operon. The authors previously cloned and sequenced the genes encoding the active class Ib RNR of and showed that these genes are clustered in an atypical region, which differs from that of other known class Ib enzymes because of an intergenic sequence (1171 bp) present between and . This study investigated the transcriptional organization and regulation of this region by RT-PCR. Three different and independent mRNA were found (, and an ORF present in the intergenic region), each one being transcribed from its own promoter and being essential for normal growth. The ratio of to mRNA was 9·1, as determined by competitive RT-PCR; the expression of both and was found to be dependent on the culture growth phase, and was induced in the presence of hydroxyurea, manganese and hydrogen peroxide. This is believed to be the first direct evidence for a manganese-dependent transcriptional regulation of genes. These results suggest a common and coordinated regulation of the different genes, despite their being transcribed from independent promoters.

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2003-04-01
2024-12-06
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