Massive Amplification at an Unselected Locus Accompanies Complex Chromosomal Rearrangements in Yeast

Gene amplification has been observed in different organisms in response to environmental constraints such as limited nutrients or exposure to a variety of toxic compounds, conferring them specific phenotypic adaptations by increased expression levels. But the presence of multiple gene copies has generally not been found in natural genomes in absence of specific functional selection. Here we show that the massive amplification of a chromosomal locus (up to 880 copies per cell) occurs in absence of any direct selection, associated with low-order amplifications of flanking segments in complex chromosomal alterations. These results were obtained in the mutants with restored phenotypes that spontaneously appeared from genetically engineered strains of the yeast Saccharomyces cerevisiae suffering from severe fitness reduction. Grossly extended chromosomes (macrotene) were formed, with complex structural alterations but sufficient stability to propagate unchanged over successive generations. Their detailed molecular analysis, including complete genome sequencing, identification of sequence breakpoints and comparisons between mutants revealed novel mechanisms to their formation whose combined action underlies the astonishing dynamics of eukaryotic chromosomes and its consequences./p>

from Genetics via xlomafota13 on Inoreader http://ift.tt/1UGX5ZZ
via IFTTT