- Volume 70, Issue 1, 1972

The association of invertase with Neurospora wall was studied biochemically in six cytologically distinct stages of the Neurospora asexual life-cycle: (i) conidia, (ii) mid-log phase [10 h old], (iii) post-log phase hyphae [18 h old], (iv) aerial mycelium [4 days old], (v) submerged mycelium [4 days old], and (vi) mycelium [2 days old] induced to form conidiophores. The percentages of total invertase activity found in the wall fraction were 8, 18, 23, 8, 21 and 17, respectively. The specific activities of the wall fraction were 3, 85, 120, 40, 24, and 74 units of invertase activity per milligram protein, respectively. Histochemical localization of invertase with an indirect immunofluorescent technique also showed that conidiophores had strong activity in their walls as well as in the cytoplasm and that vacuoles were devoid of any activity.

Summary: The production of a rennin-like milk-clotting enzyme by Penicillium citrinum 805 was investigated. Corn-steep water was the best medium for the production of the enzyme. Dephytinization of corn-steep water lowered production of the enzyme. The extent of mycelial sporulation was correlated with the milk-clotting activity. Precipitation with ammonium sulphate and ethanol was unsuitable, but acetone produced active fractions. The enzyme action was optimal at 60° and at pH 6·0 while the stability of the enzyme was maximal at pH 5·37. The enzyme exhibited feeble proteolytic activity.

Seventy-three cysteine (cys) auxtrophs of Proteus mirabilis strain 13 were arranged in six transductional groups. Members of these groups had nutritional requirements similar to Salmonella typhimurium and Escherichia coli cys mutants. The chromosomal topography of the P. mirabilis mutants resembles that of S. typhimurium and E. coli cys mutants in that they are not arranged in an operonand cysB mutants are co-transducible with tryptophan markers. The P. mirabilis cysG auxotrophs may be equivalent to S. typhimurium cysI and J mutants which have similar nutritional requirements. In P. mirabilis cysG is closely linked to cysC and the S. typhimurium cysC, D, H, I, J cluster may also be present in this organism. The P. mirabilis cysE mutants, which are co-transducible with an arginine gene cluster, seem to lack O-acetylserine sulphhydrylase activity.

The Escherichia coli k, b and phage P1 host specificity genes (hsp) were introduced into Salmonella typhimurium by means of E. coli Hfr × S. typhimurium F− crosses. The three systems were found to govern modification and restriction of phages P22 and L. The restriction coefficients were comparable to that of λ for the PI system and were lower (about 100) for the k and b systems. Phage grown on hspK+ and hspB+ recombinants was restricted by S. typhimurium independently of the restriction governed by the lt system. This observation suggested that S. typhimurium possesses a previously undetected hsp locus allelic to those of E. coli k and b.

SUMMARY: A strain of yeast called 2nl is described which behaved genetically as a diploid, but had approximately 18 % less DNA than a normal diploid. It produced apparently normal haploid ascospore cultures, which had approximately 20 % less DNA than normal haploids. The growth of 2nl from low yeast concentrations was normal, but at high concentrations it was abnormal; viability was not affected. The timing of DNA synthesis in a synchronously dividing culture was in the usual position in the growth cycle for yeast. DNA was estimated by the diphenyl-amine reaction; there was no special effect on this reaction, peculiar to 2nl and its ascospore cultures. DNA values were confirmed by A 260 measurements. The yeast 2nl was more sensitive to both gamma and u.v. radiations than were normal diploids and there was some indication that defective repair processes were involved.

Summary: Various features of the growth curve of a synchronous culture of bacteria are related to the generation time distribution of the cells, and the parent-progeny generation time correlation coefficients. It is suggested that the examination of synchronous growth enables the parameters of the generation time distribution, and the correlation coefficients, to be extracted relatively simply and their dependence upon environment to be investigated. Methods of estimating the degree of synchronization, and some corrections for the effects of imperfect synchronization, are suggested.

Summary: The shape of the generation time distribution of Escherichia coli b/r organisms in a state of balanced growth, and the parent-daughter generation time correlation coefficient have been extracted from growth data obtained with a synchronously dividing culture. The numerical techniques employed are described. The method is simple and yields results that are more accurate than those obtained previously.

Glycerol-accelerated death of starved, glycerol-limited populations of Klebsiella aerogenes occurred if the medium used to assess viability contained glycerol, but not if it contained pyruvate or glucose. Pyruvate-accelerated death of glycerol-limited populations occurred with all three types of recovery medium. Lactose-limited populations showed lactose-accelerated death, with comparable substrate and recovery medium specificity, without change in β-galactosidase content. Inducers of the lac operon, whether gratuitous or not, also accelerated death of lactose-limited populations. Cyclic AMP (0·08 mm) or its butyryl derivative (0·02 mm), but not a variety of other nucleotides, prevented substrate-accelerated death but did not abolish the prolonged lags characteristic of survivors of this stress; these findings further support the view that substrate-accelerated death is related to intracellular repression-derepression processes.