ORGANIZATIONAL CHARACTERISTICS AND INFORMATION-CONTENT OF AN ARCHAEALGENOME - 156 KB OF SEQUENCE FROM SULFOLOBUS-SOLFATARICUS P2

We have initiated a project to sequence the 3 Mbp genome of the thermo acidophilic archaebacterium Sulfolobus solfataricus P2. Cosmids were s elected from a provisional set of minimally overlapping clones, subclo ned in pUC18, and sequenced using a hybrid (random plus directed) stra tegy to give two blocks of contiguous unique sequence, respectively, 1 00 389 and 56 105bp. These two contigs contain a total of 163 open rea ding frames (ORFs) in 26-29 putative operons; 56 ORFs could be identif ied with reasonable certainty. Clusters of ORFs potentially encode pro teins of glycogen biosynthesis, oxidative decarboxylation of pyruvate, ATP-dependent transport across membranes, isoprenoid biosynthesis, pr otein synthesis, and ribosomes. Putative promoters occur upstream of m ost ORFs. Thirty per cent of the predicted strong and medium-strength promoters can initiate transcription at the start codon or within 10 n ucleotides upstream, indicating a process of initial mRNA-ribosome con tact unlike that of most eubacterial genes. A novel termination motif is proposed to account for 15 additional terminations. The two contigs differ in densities of ORFs, insertion elements and repeated sequence s; together they contain two copies of the previously reported inserti on sequence ISC1217, five additional IS elements representing four nov el types, four classes of long non-IS repeated sequences, and numerous short, perfect repeats.