Genome organization of the linear cytoplasmic element pPE1B from Pichia etchellsii

The linear cytoplasmic element pPE1B from Pichia etchellsii CBS2011 (synony m Debaryomyces etchellsii) mas totally sequenced. It consists of 12835 bp a nd has a remarkable high A + T content of 77.3%, The termini of pPE1B were found to consist of inversely orientated identical nucleotide repetitions 1 61 base pairs long, to which proteins are probably covalently linked at the 5 ' ends. Ten putative genes (open reading frames, ORFs) were identified, covering 96.5% of the total sequence. The predicted polypeptides correspond to proteins encoded by ORFs 2-11 of the linear plasmids pGKL2 of Kluyverom yces lactis and pSKL of Saccharomyces kluyveri. ORF1, existing on both latt er elements, is lacking on pPE1B, An upstream conserved sequence motif (UCS ) is located at the expected distance from the start codon of each of the 1 0 ORFs. As the arbitrarily chosen UCS6 was able to drive expression of a re porter gene in the heterologous pGKL-encoded killer system of K. lactis, ex tranuclear promoter function is probable. The almost congruent genome organ ization of pPE1B and other autonomous linear yeast plasmids sequenced so fa r, i.e. pGKL2 and pSKL, suggests a common, presumably viral, ancestor. The sequence of pPE1B has been submitted to the EMBL data library under Accessi on No. AJ278986, Copyright (C) 2001 John Wiley & Sons, Ltd.