Conjugation is a plasmid-encoded DNA transfer process requiring specific cellular contacts between donor and recipient cells. It has been demonstrated that conjugative transfer can occur between E.coli and several yeast species. Such trans-kingdom transfer raises many questions concerning the broader evolutionary consequences of conjugation, the nature of cellular interactions, and the fate of the transferred DNA. We have studied the E.coli-yeast transfer of a range of bacterial plasmids and have found that the transfer of the plasmid RP4 was most efficient, and requires the same bacterial genes as transfer between E.coli cells. Current work is aimed at identifying yeast factors important for transfer. We have shown that transfer occurs independent of both the growth state of the recipient cell, and the stage of the cell cycle. However transfer is more efficient to haploids rather than diploids. We have isolated seven UV induced yeast mutants defective in their ability to act as recipients in conjugation. One of which is insensitive to alpha factor and therefore does not form diploids. Mutant con1 has been most extensively characterised, it is a recessive mutation in a single gene, and shows a 40 fold reduction in transfer efficiencies compared to wild type. This decrease in transfer efficiency correlates to an increased sensitivity to cell wall degrading enzymes, suggesting that this mutant has altered cell wall properties. We are attempting to clone the wild type CON1 allele using mutant rescue with a yeast genomic library.