Promoter activity associated with the left inverted terminal repeat of the killer plasmid k1 from yeast

Abstract

The killer plasmid k1 of Kluyveromyces lactis has terminal inverted repeats of 202 base pairs (bp). The left terminal repeat is contiguous to the transcribed open reading frame, ORF1, which is supposed to code for a DNA polymerase. A 266-bp fragment (called P k1 containing most of the terminal repeat sequence was isolated and examined for promoter activity. P k1 was fused, in either original or inversed orientation, with a promoter-less lacZ gene of E coli and a promoter-less G418 resistance gene of Tn 903. These fusions were introduced into a pKD1-derived circular vector, and transformed into a lactose-negative ( lac4), and a G418-sensitive K lactis host. Lac+ and G418-resistant transformants were obtained with either orientation of P k1.The promoter activity of P k1 fragment was independent of the presence or absence of killer plasmids. It is not known whether P k1 can also function bidirectionally on the natural k1 plasmid. The possible functions of P k1 for killer plasmid gene expression and plasmid replication are discussed.