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Sex-linked, recessive, cold-sensitive mutants of Drosophila melanogaster : genetic and biochemical studies Mayoh, Helen Margaret


Cold-sensitive mutants of E. coli have been valuable in the study of the structure and assembly of bacterial ribosomes. Some cold-sensitive mutations of E. coli have been mapped to loci coding for ribosomal proteins. Other cold-sensitive mutations have been shown to alter the regulatory properties of bacterial enzymes. In contrast, little was known about the genetics and biochemistry of cold-sensitive mutants of Drosophila and other eukaryotes. Also, the genetic loci of ribosomal proteins of D. me1anogaster were unknown although the ribosomal RNA genes have been located on the X and 2nd chromosomes. Therefore the following questions were asked: Can cold-sensitive lethals of the X chromosomes of Drosophila melanogaster be isolated? If so, what are their genetic properties? Do some have altered ribosomal proteins as in cold-sensitive mutants of bacteria? The study was part of a general search for and characterization of cold-sensitive lethals of all the chromosomes of D. melanogaster. Among 3,919 EMS-treated X chromosomes, 25 were retained as cold-sensitive lethals or semi-lethals. That is, more than 20% of the flies carrying a cold-sensitive lethal survived at 22°C and none at 17°C, and for cold-sensitive semi-lethals, > 30% survived at 22°c and <13% at 17°c. The cold-sensitive mutations were not randomly distributed, 7 being located at the X tip and 3 being alleles to the right of car. Over half exhibited female sterility at the permissive temperature and 7 exhibited visible phenotypes characteristic of bobbed and Minute mutations. As the presence of altered ribosomal proteins has been demonstrated in cold-sensitive mutants of bacteria, the ribosomal proteins from Drosophila mutants and controls were studied by 2-dimensional gel electrophoresis. By this method, it was estimated that 69-72 proteins are present in the ribosomes of Drosophila. No qualitative differences were observed in the gel patterns of ribosomal proteins from 5 cold-sensitive, sex-linked mutants and the controls. A summary of the biochemical testing of the ribosomes from other cold-sensitive mutants of Drosophila is also given. No biochemical evidence to support the hypothesis that cold-sensitive mutants of Drosophila have altered ribosomes was obtained. The limitations of the study and recommendations for future research are discussed.

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