Similar-sized daughter-strand gaps are produced in the leading and lagging strands of DNA in UV-irradiated E. coli uvrA cells.

The nascent DNA synthesized after UV irradiation contained discontinuity, i.e., daughter-strand gaps. The sizes of these gaps produced in the leading and lagging strands of UV-irradiated Escherichia coli cells were determined by using strand-specific DNA probes. The DNA isolated from irradiated uvrA delta(lac-pro) cells was hybridized with the 32P-labeled single-stranded DNA probes. After digestion with S1 nuclease, the sizes of the bound radioactive DNA fragments were determined by electrophoresis in an alkaline agarose gel. It was found that the average size of gaps produced in the leading strand was about 0.12 kb, whereas those produced in the lagging strand was slightly smaller than 0.12 kb. No gaps larger than 0.5 kb were detected.     

Focal increases in [Ca]i may account for apparent low Ca sensitivity in swine carotid artery

Estimates of [Ca²⁺]_i sensitivity in intact smooth muscle are frequently obtained by measuring [Ca²⁺]_i with indicators such as aequorin or Fura-2. We investigated whether focal in increases in [Ca²⁺]_i could impair such measures of [Ca²⁺]_i sensitivity. Stimulation of swine carotid artery with 10 μM histamine increased aequorin estimated [Ca²⁺]_i, Fura-2 estimated [Ca²⁺]_i and Ca²⁺ sensitivity without significantly altering the aequorin/Fura-2 ratio (an estimate of [Ca²⁺]_i homogeneity). Subsequent inhibition of Na⁺/Ca²⁺ exchange by replacement of Na⁺ in the PSS with choline⁺ significantly increased aequorin-estimated [Ca²⁺]_i but only minimally increased Fura-2 estimated [Ca²⁺]_i, myosin light chain (MLC) phosphorylation and force. This resulted in a large increase in the aequorin/Fura-2 ratio, suggesting an increase in [Ca²⁺] inhomogeneity. Addition of 100 μM histamine to tissues in the choline⁺ buffer initially increased both aequorin and Fura-2 estimated [Ca²⁺]_i but after 10 min exposure both of the [Ca²⁺]_i estimates declined to pre-histamine levels. Histamine addition significantly increased MLC phosphorylation and force, indicating increased Ca²⁺ sensitivity, but the aequorin/Fura-2 ratio remained elevated and uncharged from pre-histamine values. These data show that under certain conditions, aequorin and Fura-2 can yield widely differing estimates of [Ca²⁺]_i, and thus can cause misleading assessments of Ca²⁺ sensitization mechanisms. These discrepancies may arise from inhomogeneous or focal increases in [Ca²⁺]_i which can be evaluated with the aequorin/Fura-2 ratio.     

A 43 kDa DNA binding protein from the pea chloroplast interacts with and stimulates the cognate DNA polymerase.

A DNA binding protein with DNA polymerase 'accessory activity' has been identified and purified to apparent homogeneity from pea chloroplasts. This protein consists of a single subunit of 43 kDa and binds to DNA regardless of its base sequence and topology. It increases cognate DNA polymerase-primase activity in a dose dependent manner. Using solid phase protein-protein interaction trapping and co-immunoprecipitation techniques, the purified protein was found to associate with the chloroplast DNA polymerase. The chloroplast DNA polymerase also binds directly to the radioiodinated 43 kDa protein. The specific interaction between 43 kDa protein and chloroplast DNA polymerase results in the synthesis of longer DNA chains. The 43 kDa protein, present abundantly in the pea chloroplast, appears to increase processivity of the chloroplast DNA polymerase and may play an important role in the replication of pea chloroplast DNA.     

粒粒橙饮料的分层与汁胞萎瘪褪色的初步研究

本文研究了热因子对琼脂悬浮稳定性的影响,分析了造成汁胞萎瘪褪色的原因,并提出了解决的办法。认为只要琼脂的加热时间不要太长,分层现象是比较容易解决的。海藻酸钙凝胶薄膜和含油溶剂预处理能很好地防止汁胞的萎瘪破碎,但操作不当容易造成褪色。     

胰岛素诱导低血糖大鼠心房肌细胞特殊颗粒的形态计量和心房利钠肽免疫组织化学研究

通过形态计量学和免疫组织化学方法发现胰岛素诱导低血糖大鼠心房肌细胞核周区特殊颗粒（ＡＳＧ）的体密度、面数密度和数密度及平均直径均高于对照组（Ｐ＜０．０５）,但高尔基复合体各参数与对照组比较没有差别（Ｐ＞０．０５）。实验组的心房利钠肽（ＡＮＰ）的免疫反应强度比对照组强（Ｐ＜０．００１）。提示胰岛素诱导低血糖对心房利钠肽的释放具有抑制作用,表明ＡＮＰ作为生理和病理调节递质与代谢刺激相拮抗。     

苏芸金杆菌发酵生产工艺改进研究：Ⅰ芽孢接种和营养体接种比较

苏芸金杆菌液体深层发酵中用营养体接种二级发酵工艺和用二级发酵初期培养物作种子进行三级发酵工艺是可行的。试验结果表明：二级发酵种子罐营养体最佳移种茵龄为９ｈ左右,此时营养体数量多、整齐、染色均匀,显微镜下菌体有折光点存在,三级接种营养体菌龄约为４ｈ左右,菌体数量多,同步率高,少量染色不均匀。发酵液含菌数和发酵产品毒力均达到芽抱接种相同水平,但生产周期明显缩短４－５ｈ,因此相应提高发酵罐生产能力２０％。     

人鼻咽癌细胞基因组中瘤基因Ha－ras－1的Dnase Ⅰ超敏感位点的初步研究

ＤＮａｓｅⅠ超敏感位点的研究能够发现潜在的调控基因转录活化的位点,比较正常人外周血有核细胞,淋巴瘤细胞株Ｐ３ＨＲ１和人鼻咽癌低分化磷癌细胞株ＨＯｎＥ１和ＨＮＥ２中Ｈａ－ｒａｓ－１瘤基因的ＤＮａｓｅⅠ超敏感位点发现,只有ＨＯＮＥ１和ＨＮＥ２细胞基因组中存在一个ＤＮａｓｅⅠ超敏感位点,位于第一个外显子上游０．３７ｋｂ处,上述结果提示正常白细胞和Ｐ３ＨＲ１细胞中Ｈａ－ｒａｓ－１基因处于失活状态,而在鼻咽癌细胞基因组中则处于活化状态,它的活化可能与０．３７ｋｂ处的ＤＮＡ序列有密切的关系。