HIGH-MOBILITY GROUP I(Y)-LIKE DNA-BINDING DOMAINS ON A BACTERIAL TRANSCRIPTION FACTOR

The bacterium Myxococcus xanthus responds to blue light by producing c arotenoids. It also responds to starvation conditions by developing fr uiting bodies, where the cells differentiate into myxospores. Each res ponse entails the transcriptional activation of a separate set of gene s. However, a single gene, carD, is required for the activation of bot h light- and starvation-inducible genes. Gene carD has now been sequen ced. Its predicted amino acid sequence includes four repeats of a DNA- binding domain present in mammalian high mobility group I(Y) proteins and other nuclear proteins from animals and plants. Other peptide stre tches on CarD also resemble functional domains typical of eukaryotic t ranscription factors, including a very acidic region and a leucine zip per. High mobility group yI(Y) proteins are known to bind the minor gr oove of A+T-rich DNA. CarD binds ill vitro an A+T-rich element that is required for the proper operation of a carD-dependent promoter in viv o.