RANDOM SEQUENCE-ANALYSIS OF GENOMIC DNA OF A HYPERTHERMOPHILE - AQUIFEX PYROPHILUS

Aquifex pyrophilus is one of the hyperthermophilic bacteria that can g row at temperatures up to 95 degrees C. To obtain information about it s genomic structure, random sequencing was performed on plasmid librar ies containing 0.5-2kb genomic DNA fragments of A. pyrophilus. Compari son of the obtained sequence tags with known proteins revealed that 12 3 tags showed strong similarity to previously identified proteins in t he PIR or Genebank databases. These included three proteases, two amin o acid racemases, and three enzymes utilizing oxygen as substrate. Alt hough the GC ratio of the genome is about 30%, the codon usage of A. p yrophilus showed biased occurrence of G and C at the third position of codons, especially those for amino acids such as asparagine, aspartic acid, cysteine, glutamine, glutamic, acid, histidine, lysine, and tyr osine. A higher ratio of positively charged amino acids in A. pyrophil us proteins as compared with proteins from mesophiles suggested that A quifex proteins might contain increased ion-pair interaction that coul d help to maintain heat stability.