The presence of a defective LEU2 gene on 2 mu DNA recombinant plasmids of Saccharomyces cerevisiae is responsible for curing and high copy number

Abstract

The copy number of 2 mu DNA-derived plasmids in CIR+ Saccharomyces cerevisiae transformants is determined by its selective marker and is usually much lower than that of the endogenous plasmid. Only plasmids containing the leu2 allele of pJDB219, designated as leu2-d, under selective conditions displayed a higher copy number than did endogenous 2 mu DNA and by displacement generated cured cells. Spontaneous loss of 2 mu DNA occurred with a frequency of about 0.02% per generation. Curing plasmids, like pMP78, have copy numbers of 35; noncuring plasmids, like pDB248 or YEp6, have copy numbers of 4 to 8. The 2 mu DNA copy number in strains AH22 and YNN27 were determined to be 40 and 100, respectively. The high copy number of leu2-d-containing plasmids can be explained by its weak expression of less than 5% that of the wild-type LEU2 gene. The leu2-d allele has a deletion of the 5'-end sequence starting from 29 base pairs before the ATG initiation codon, but surprisingly, its expression is still regulated. On YRp7, which contains the chromosomal autonomic replication sequence ARS1, the defective leu2-d allele could not complement a leu2 host strain. This suggests a more stringent control of replication of ARS1-containing plasmids than of 2 mu-containing plasmids.

A new system for amplifying 2 μm plasmid copy number in Saccharomyces cerevisiae

“…The selection for higher 2|im copy number in our system is based solely on the growth temperature. This is in contrast to the system described by Erhardt and Hollenberg (1983), whereby cells increase their 2jim copy number under special selection conditions in minimal media without leucine because of the dependence on a weakly expressed LEU2 gene (dLEU2 allele). By changing growth temperature we can obtain different levels of plasmid copy number and in this way may achieve more flexibility in fine tuning expression yields.…”

The β-1,6-glucan containing side-chain of cell wall proteins of Saccharomyces cerevisiae is bound to the glycan core of the GPI moiety

“…proAB, luci"ZAM 151) [6]. The Succhuromyces cerevisiue yeast strain used was SU51 (YT6-2-1 L) MA Ta, cir+, leuZ-3,112, his4519, cunl [7]. Both strains were grown and transformed as described previously [8].…”

Vectors for rapid selection of integrants with different plasmid copy numbers in the yeast Hansenula polymorpha DL1

“…In contrast, plasmids bearing the homologous H. polymorpha URA3 gene usually integrate into the genome in a single copy number. The same is true for S. cerevisiae, since a partially defective selective marker (LEU2-d) was shown to increase the plasmid copy number in this yeast (Erhart and Hollenberg, 1983). Altogether, these data indicate that the plasmid copy number in transformants is roughly dependent on the strength of selective pressure.…”