Three structural proteins, TP1, TP2 and TP3, of the virus TTV1 of the thermophilic archaebacterium Thermoproteus tenax strain Kra1 were mapped within the viral genome by locating the amino-terminal amino acid sequences of these proteins in the TTV1 DNA sequence. The derived amino acid sequences comprise 113, 139 and 160 amino acid residues, respectively. All three proteins are hydrophobic. The three genes are not linked, but transcribed in the same direction. No Shine-Dalgarno sequences are found in the vicinity of the initiation codons of these three genes. By Northern analysis, four mRNAs of 0.5 kb, 0.8 kb, 1.1 kb and 1.8 kb in size were found to be encoded in the region and in the vicinity of the genes, the shortest one (t1) encoding TP3 and the longest one (t4) encoding TP2. No transcript from the region encoding TP1 has been found so far. A transcriptional start site was mapped for the transcript t1. Its upstream sequence was similar to the putative consensus sequence for archaebacterial promoters.
Six variants of the TTV1 genome, including the primary isolate, have been characterized. DNA sequence comparison of 'wild-type' virus (WT) and one of the variants (VT3) showed that differences are due to insertions and deletions that were confined to contiguous portions of two distinct ClaI fragments. Seven similar short DNA sequences (30-102 bp) were involved in the variation. The deletions and insertions of these short DNA sequences occurred in every case adjacent to the 8 bp consensus sequence 5'-ACXCCTAC-3' which formed the 5' flank of the segments involved.
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