Amplification of a gene for metallothionein by tandem repeat in a strain of cadmium-resistant yeast cells

Abstract

In a cadmium‐resistant strain of Saccharomyces cerevisiae, cells are protected against cadmium toxicity by the production of large amounts of cadmium‐binding metallothionein, as occurs similarly in a copper‐resistant strain. The apoprotein of the metallothionein is encoded by the CUP1 gene on chromosome VIII. The CUP1 gene is present as 8–10 copies in the cadmium‐resistant strain as a result of tandem repeat of a 2.0‐kb fragment of DNA that includes CUP1, while the wild‐type strain contains only a single copy of CUP1. In the cadmium‐resistant strain, some evidence for elongation of chromosome VIII with variations in length (maximum to 200 kb) was obtained. However, the elongation was not due to the tandem repeats of the CUP1‐containing region.

Selection in the evolution of gene duplications

“…Gene duplication may be a temporary mechanism to increase protein or RNA dosage, as in the case of rRNA genes in amphibian oocytes and ciliate macronuclei, the chorion genes in some dipterans, actin genes in chicken as well as drug transporters in somatic tissues (see [34,37] for reviews). Protein dosage effects have also been demonstrated in a number of other studies of inheritable adaptive gene duplications [32,34,35,43,44,46,49,51,53,61]. Furthermore, there is evidence from the analysis of the yeast genome that duplicated genes tend to be from those sets of functions that are more highly expressed [62], supporting a general role for selection on protein dosage in duplicated genes.…”

“…Although the notion of duplication producing redundant genes is central to current theories of duplicated gene evolution, the short-term benefits of gene duplications are well known. This is illustrated by the numerous observations of adaptive gene amplifications in response to antibiotics [ 31 , 32 , 33 ], anticancer drug treatments and exposure to various toxins [ 34 , 35 , 36 , 37 , 38 , 39 ] or heavy metals [ 40 , 41 , 42 , 43 , 44 ], nutrient limitations [ 32 , 33 , 45 , 46 , 47 , 48 , 49 , 50 ], pesticide treatments [ 51 , 52 , 53 ], extreme temperatures [ 54 , 55 ] and symbiotic and parasitic interactions [ 56 , 57 ]. Combining this information with the observations that recently duplicated genes evolve under purifying selection ([ 21 ] and our present work), it seems reasonable to hypothesize that a majority of duplicated genes that achieve fixation in a population increase fitness when present in two or more copies in a genome and thus are subject to purifying selection from the moment of duplication.…”

The molecular evolution of spiggin nesting glue in sticklebacks

“…Gene duplication can lead to an increase in protein product andfollowing the divergence of duplicated genesnovel protein functions (Ohno 1970;Lynch & Force 2000) and lineage-specific traits (Wu et al 2009;Vonk et al 2013). Studies of bacteria (Hastings et al 2000;Riehle et al 2001), protists (Kaufmann & Klein 1992;Reinbothe et al 1993), fungi (Tohoyama et al 1996;Brown et al 1998), plants (van Hoof et al 2001Widholm et al 2001) and invertebrates (Otto et al 1986;Lenormand et al 1998) have demonstrated that gene duplication can play a significant role in adaptive evolution. In primates, the accelerated expansion of several gene families also suggests evidence for adaptive evolution (Hahn et al 2007).…”

Rapid identification of mRNA processing defects with a novel single-cell yeast reporter

“…Although this reporter has proved to be instrumental in examining cis-pre-mRNA splicing elements and transacting factors, it does have limitations. Most notably the endogenous nonessential CUP1 gene is often present in two or more copies present in most laboratory strains (Karin et al 1984;Tohoyama et al 1996), requiring that all genomic copies of this gene be removed in order to specifically query premRNA splicing efficiency. Additionally, after the high-copy reporter is introduced into cells, the data derive from growth on solid media containing an ensemble population of cells.…”