CONTRASTING PATTERNS OF EVOLUTIONARY DIVERGENCE WITHIN THE ACINETOBACTER-CALCOACETICUS PCA OPERON

The six enzymes required for catabolism of protocatechuate to succinat e and acetylCoA are encoded by the pen genes in the Gram(-) bacterium, Acinetobacter calcoaceticus. The clustered A. calcoaceticus cat genes encode an analogous set of enzymes associated with the metabolic diss imilation of catechol. The nucleotide (nt) sequences of pcaIJFB and pc aK, reported here, complete evidence showing that all of the pen struc tural genes are tightly grouped in the order pcaIJFBDKCHG within a sin gle operon. The pcaIJF region is nearly identical in nt sequence to th e A. calcoaceticus catIJF region which exhibits a G+C content and a co don usage pattern exceptional for A. calcoaceticus. In contrast, pcaD, pcaC, pcaH and pcaG have diverged substantially from their evolutiona ry counterparts in the cat region; all of these divergent genes exhibi t G+C contents and codon usage patterns that are typical for A. calcoa ceticus. The pcaIJF and catIJF regions are known to exchange DNA seque nce information, and this property may have contributed to their nt se quence conservation. The pcaK gene has no counterpart among known cat genes. The deduced amino-acid sequence of PcaK indicates that it may b e a transmembrane protein associated with transport.