Streptomycin-resistant Escherichia coli mutant temperature sensitive for the production of Qbeta-infective particles.

A streptomycin-resistant Escherichia coli mutant has been isolated that is temperature sensitive for Qbeta phage, but not for the group I RNA phages f2, MS2, and R17. The growth of Qbeta in the mutant at the nonpermissive temperature (42 degrees C) results in the release of a near-normal burst of noninfectious particles that cosediment with Qbeta in a sucrose gradient. It is assumed that the mutant is defective at elevated temperatures in the suppression of nonsense codons, thereby producing Qbeta-like particles which are noninfectious because of the lack of the read-through protein A1.     

Escherichia coli mutant temperature sensitive for group I RNA bacteriophages.

The temperature-sensitive conjugational transfer-deficient mutant Escherichia coli JCFL39, carrying a traD(Ts) mutation, is herein described as also being temperature sensitive for group I RNA phages (MS2, f2, and R17) but not for Q beta. Temperature shift experiments showed that the growth of group I phage MS2 in the mutant could be inhibited by a post-penetration event at high temperature. A possible role for the traD cistron of sex factor F in the intracellular development of MS2 is suggested.     

Studies on ribosomal protein biosynthesis in an RNA polymerase temperature sensitive E. coli mutant.

Summary In E. coli strain XH56 the synthesis of all RNA species is blocked upon shifting the culture to the non-permissive temperature. The decay of specific messenger RNA species coding for individual ribosomal (r) proteins was followed by measuring the rate of r-protein synthesis by pulse labelling at various times after the shift. The half-lives of the average 30S r-protein and 50S r-protein mRNA species are identical (1.75 min) and shorter than those of the average messenger coding for total cell proteins (2.75 min). Most individual r-protein messengers have a half-life in the same range (1.50–2.00). Only a few r-protein messengers have significantly longer half-lives: S1 (2.80 min), S17 (3.29 min), L29 (2.30 min), L31 (2.30 min), L32 (2.33 min) and L16 (2.60 min). The results indicate that the degradation of most individual r-protein mRNA species is not specifically controlled.After a few min at the non-permissive temperature, all protein synthesis is blocked. The restart of r-protein synthesis was followed after shifting the culture back to the permissive temperature. The recovery of cell growth is very slow. During this period preferential r-protein synthesis was observed. Moreover differential rates of biosynthesis of r-proteins was obtained, it may be indicative of specific regulatory process(es).     

越冬针叶有机自由基产额对低温和光照的反应

以越冬针叶树苗木针叶为材料在黑暗与强光照两种条件下用ESR波谱仪检测有机自由基信号强度对不同温度的反应。结果表明:1.越冬伤害越重,针叶有机自由基产额越高;2.有机自由基产额随温度下降而增加;3.光照对有机自由基产额有明显的增强作用,且此增强作用在0℃表现最明显;4.自由基清除剂维生素C对有机自由基的产生有明显的抑制作用。据此认为红松苗的越冬伤害和有机自由基的高产额有关。在自然界针叶有机自由基的高产额主要和冬季的强日照有关,但低温也有一定作用。     

低温及光照对红苞蔓绿绒幼苗膜脂过氧化的影响

本文研究低温和光照条件对红苞蔓绿绒幼苗膜脂过氧化作用的影响。目测结果表明,红苞蔓绿绒幼苗叶片受低温伤害程度与对照差异不明显,且各处理间差异不显著。各处理的丙二醛含量基本上高于对照,细胞膜透性、过氧化氢酶和过氧化物酶活性均高于对照,说明红苞蔓绿绒幼苗具有较高的抗低温能力,膜脂过氧化水平随低温胁迫强度的增强而增大,过氧化氢酶和过氧化物酶活性与丙二醛含量成正相关。5℃时,在光照条件下幼苗的细胞膜透性、丙二醛含量、过氧化氢酶和过氧化物酶活性均高于暗处理;但10℃时结果却相反。     

Light sensitivity of plastids and plastid pigments present in the albescent maize mutant

Dark grown albescent corn seedlings are deficient in colored carotenoids but accumulate phytoene, phytofluene and an unidentified substance in the carotenol fraction. They bleach upon exposure to bright light and appear albino. Seedlings grown under low level incandescent light are normal in appearance and contain almost as much colored carotenoid as control seedlings. The existing leaf tissue of seedlings grown under low level light does not bleach upon exposure to bright light. The enhanced carotenoid synthesis and stabilization of plastids is not affected by brief illumination with red light but requires several hours of low level incandescent light.     

Studies on light absorption and photochemical activity changes in chloroplast suspensions and leaves due to light scattering and light filtration across chloroplast and vegetation layers

An experimental analysis is presented concerning the effect on relative light absorption by the two photosystems caused by (a) a highly light scattering environment (the detour effect) and (b) light filtration across successive chloroplast layers (the light attenuation effect). Both suspensions of isolated chloroplasts and leaves were employed.It is concluded that within a single spinach leaf these phenomena are likely to lead to only rather small increases in relative photosystem I absorption and activity with respect to photosystem II and will thus not exert a significant effect on non cyclic electron transport. On the contrary when light is filtrated across successive vegetation layers (shade light) significant increases in the relative PSI absorption and activity may be encountered.It is determined that the detour effect in mature leaves from a variety of plants increases overall photosynthetically useful light absorption by 35–40%.Abbreviations F_M maximal fluorescence - LHCP₂ light-harvesting chlorophyl a/b protein complex II - Q_A-primary quinone acceptor of photosystem II     

Processing of ribosomal RNA in a temperature sensitive mutant of BHK cells.

The processing of ribosomal RNA has been studied in a temperature sensitive mutant of the Syrian hamster cell line BHK 21. At 39 degrees C, these cells are unable to synthesize 28S RNA, and 60S ribosomal subunits, while 18S RNA, and 40S subunits are produced at both temperatures. At 39 degrees C the 45S RNA precursor is transcribed and processed as in wild type cells. The processing of the RNA precursors becomes defective after the cleavage of the 41S RNA, and the separation of the 18S and 28S RNAs sequences in two different RNA molecules. The 36S RNA precursor, which is always present in very small quantity in the nucleoli of wild type cells and of the mutant at 33 degrees C, is found in very large amounts in the mutant at 39 degrees C. The 36S RNA can be, however, slowly processed to 32S RNA. The 32S RNA cannot be processed at 39 degrees C, and it is degraded soon after its formation. Only a small proportion accumulates in the nucleoli. The 32S RNA synthesized at 39 degrees C cannot be processed to 28S RNA upon shift to the permissive temperature, even when the processing of the newly synthesized rRNA has returned to normal. The data suggest that the 36S and 32S RNAs are contained in aberrant ribonucleoprotein particles, leading to a defective processing of the particles as a whole.     

Studies of adaptation of influenza viruses to their replication in low temperature. I. Biological properties

Influenza A/H3N2/ virus strains derived from various isolations and replicated in lowered temperatures (37 degrees, 35 degrees, 33 degrees, 30 degrees) in chicken embryos were used for the study. An alteration of temperature optimum of neuraminidase activity was established after 12-15 passages of influenza virus in lowered replication temperature and it differed depending on tested strain. During adaptation process of viruses to lowered replication temperatures no correlation between neuraminidase activity and haemagglutinating titer was seen.     

Effect of leucine on the temperature sensitive phenotype of a mammalian leucyl-tRNA synthetase mutant

The concentration of leucine in the growth medium has been found to influence the expression of the temperature sensitive phenotype of a mutant of Chinese hamster ovary cells with an altered leucyl-tRNA synthetase. Plating efficiency and growth studies showed that increasing the leucine concentration allows cells to survive at normally non-permissive high temperatures and conversely decreasing the leucine concentration enhances the adverse effects of high temperature. A similar but smaller effect was noted with isoleucine. It is suggested that this observation may form the basis of a rapid test, useful in directing the investigation of the lesion in similar mutants to pathways involving specific amino acids.