Mutational and dark-repair specificities in U.V.-irradiated di-auxotrophs of E. coli B/r

Summary U.V. irradiation experiments have been performed with three tyr^-leu^- diauxotrophs of E. coli B/r; 36-10, 36-18 and 36-32. These have in common the tyr^- marker WU-36. Three types of mutations were scored; tyr⁺leu^-, tyr^-leu⁺, and tyr⁺leu⁺. The percentages of total mutants scored which are of the tyr⁺leu⁺ type depend, firstly, on the strain. The tyr⁺leu⁺ revertants are rare in 36-10 and common in 36-18 and 36-32. Secondly, the percentages of tyr⁺leu⁺ among total revertants are determined by the nature of the plating medium, being altered by supplementation with a low level of the required amino acids, a low level of nutrient broth, or by caffeine. These differential effects upon tyr⁺leu⁺ and tyr⁺leu^- or tyr^-leu⁺ reversions can be interpreted at the levels of dark-repair and the later stages in the process leading to phenotypic expression. It is suggested that states of repression and derepression may be implicated in determining susceptibility of lesions in suppressor loci to repair processes. Phenotypically different classes of mutations have different pathways leading to final expression.This work was initiated in Dr. Ruth F. Hill's laboratory, Department of Radiology, Columbia University, New York.     

Outbreak in Bristol of Conjunctivitis Caused by Adenovirus Type 8, and its Epidemiology and Control

In an investigation of an outbreak of adenovirus type 8 infection involving over 40 people it was found that the infection spread initially within the eye hospital, but subsequently involved several family contacts and two local hospitals for mentally subnormal patients. Presumptive diagnosis should be possible before subepithelial opacities have developed provided an adequate history is taken, and had that been done in this outbreak it is reasonable to suppose that many cases could have been prevented.