Biomedical subjects
Publications and source records attributed to H S Emery.
1,8-Dihydroxynaphthalene melanin in Wangiella dermatitidis and Alternaria alternata was titrated in vivo with the oxidants permanganate, hypochlorite, and H2O2. Melanized strains neutralized more oxidant and withstood higher concentrations of permanganate and hypochlorite than albino strains did. H2O2 killing required 1,000-fold higher concentrations, and melanin did not protect W. dermatitidis against H2O2.
Genetic analysis of oxygen-sensitive mutants of Cryptococcus neoformans revealed two loci (oxy1 and oxy2) linking hyperoxia sensitivity to production of melanin, a known virulence factor. Hyperoxia-sensitive strain 562 (oxy1 oxy2) is albino and avirulent. oxy2-defective strains lacking the oxy1 defect are melanin deficient but show normal hyperoxia resistance. Mutants defective at three additional mapped melanin loci fail to show hyperoxia sensitivity in the oxy1 background. Revertants of strain 562, which regain the ability to synthesize melanin by mutation at suppressor sites unlinked to oxy2, retain the oxygen sensitivity conferred by their oxy1 and oxy2 defects. These data identify the melanin gene oxy2 as unique in its association of hyperoxia resistance and melanization.
The complete nucleotide sequence of the RAD54 gene of the yeast Saccharomyces cerevisiae has been determined. The sequenced region contains an open reading frame of 2694 bp, and the predicted RAD54 protein has a potential nucleotide-binding site and possible nuclear targeting sequences. Northern analysis reveals a transcript of approx. 3.0 kb which is induced following x-ray irradiation.
Melanin formation at 37 degrees C has been proposed as a virulence factor in Cryptococcus neoformans. However, whereas catecholamine uptake is maintained at this temperature, phenoloxidase, which catalyses the oxidation of catecholamine to melanin, is severely decreased in most wild type strains cultivated at 37 degrees C.
Oxygen sensitivity mutations of Cryptococcus neoformans were mapped to three genetic loci. Three oxygen-sensitive mutants had mutations that appeared allelic and exhibited albinism tightly linked to oxygen sensitivity; these three and a fourth exhibited defects in catechol uptake and catechol oxidation to melanin. Catecholamine metabolism appears to protect C. neoformans from oxidants.
IN Dictyostelium discoideum most of the rRNA genes are known to be present as linear, extrachromosomal palindromic molecules. Here we report the identification, molecular cloning and partial DNA sequence analysis of the terminal Eco RI restriction fragment (Eco RI 1) of the rDNA. We identify a length heterogeneity confined to the most distal region of uncloned Eco RI 1, and demonstrate, by DNA sequence analysis of five independently isolated recombinant plasmids containing the Eco RI 1 fragment, that the heterogeneity can be accounted for by variable tracts of an unprecedented irregular satellite sequence with the general formula [CnT]m; n varies from 1 to 8 and accounts for the irregularity, while m varies from 18 to 34 and accounts for the length heterogeneity. The proximal [CnT]m pattern is identical (albeit irregular) in all five clones of Eco RI 1, while the distal [CnT]m sequence appears to vary between clones. Immediately proximal to the CnT satellite are found four nearly perfect tandem repeats of a 29 bp sequence. We discuss the evolution of these simple sequences at the rDNA termini and speculate about possible functions for the CnT satellite. Using the cloned terminal restriction fragment as probe, we also show that virtually all the rDNA in Dictyostelium exists in the linear palindromic form.