新疆绿蟾蜍的染色体组型初步研究

近年来,有关两栖类的染色体组型已有不少报道。无尾两栖类中蜍蟾属(Bufo)的染色体数目分为两类:2n=22和2n=20(Blain,1972)。我们对采自新疆4个地区的绿蟾蜍进行了染色体组型分析,发现其二倍体细胞染色体数均为44,是四倍体。现将我们的初步研究报道如下。     

五种雀形目鸟类核型的比较研究

染色体核型的比较研究,对于了解物种的特性,探索物种的遗传、进化、系统发育及分类地位都有一定的意义。有关鸟类的核型研究,国外已有不少报道(Castrovicja,1969; Hammar,1966,1975; Ray-Chaudhuri et al.,1969;Shidds,1982;Ta—kagi,1972等)国内在这方面的工作开展较迟,已作过核型分析的鸟类为数不多,仅见王应祥等(1982)的报道。迄今,作过核型研究的鸟类已达500多种,其中雀形目有200种。本文比较分析了五种野生雀形目鸟类的核型,它们是黑头蜡嘴雀,斑鸫,黄腹山雀,红尾伯劳和灰背椋鸟。     

大鼠发育过程中肝、肺r-GT酶活性和定位

用生物化学和组织化学方法研究正常发育中大鼠肝、肺r-GT活性和定位。结果表明:肝r-GT活性自胚龄17天开始升高,21天达高峰,出生第一天明显降低,第六天降至接近成年低水平。在胚胎期肝r-GT主要位于肝细胞内,出生后则主要位于胆小管。该结果提示胚胎期肝r-GT主要参与肝细胞膜上氨基酸的转运。出生后可能主要参与解毒功能,大鼠肺r-GT活性随发育逐步升高,主要分布于肺支气管上皮细胞。提示肺r-GT可能参与解毒功能。     

绒毛滋养层细胞直接制备染色体方法

本方法对绒毛滋养层细胞直接制备染色体作了改进。分别将制片手法,低渗液配制,秋水仙素浓度与固定时间等方面给以改良。后三者不同于Simoni及国内报道,作者认为低渗液成分,秋水仙素浓度与固定时间是不可分割与相互影响的。此法所得分裂相中,染色体形态及分散良好和显带清晰,方法稳定,有利于孕早期诊断的染色体结构分析。     

Common signal transduction system shared by STE2 and STE3 in haploid cells of Saccharomyces cerevisiae: autocrine cell-cycle arrest results from forced expression of STE2

Induction of STE2 expression using the GAL1 promoter both in a wild-type MATalpha strain and in a MATalpha ste3 strain caused transient cell-cycle arrest and changes in morphology ('shmoo'-like phenotype) in a manner similar to alpha cells responding to alpha-factor. In addition, STE2 expressed in a MATalp[ha ste3 mutant allowed the cell to conjugate with alpha cells but at an efficiency lower than that of wil-type alpha cells. This result indicates that signal(s) generated by alpha-factor in alpha cells can be substituted by signal(s) generated by the interaction of alpha-factor with the expressed STE2 product. When STE2 or STE3 was expressed in a matalpha1 strain (insensitive to both alpha- and a-factors), the cell became sensitive to alpha- or a-factor, respectively, and resulted in morphological changes. These results suggest that STE2 and STE3 are the sole determinants for alpha-factor and a-factor sensitivity, respectively, in this strain. On the other hand, expression of STE2 in an a/alpha diploid cell did not affect the alpha-factor insensitive phenotype. Haploid-specific components may be necessary to transduce the alpha-factor signal. These results are consistent with the idea that STE2 encodes an alpha-factor receptor and STE3 encodes an a-factor receptor, and suggest that both alpha- and a-factors may generate an exchangeable signal(s) within haploid cells.     

Structural transition in inactive Balbiani ring chromatin of Chironomus during micrococcus nuclease digestion

We have analysed by micrococcus nuclease digestion the chromatin structure of genes in the Balbiani ring (BR) regions of a Chironomus cell line. Gel electrophoresis of the DNA fragments reveals a repeating structure which consists of two repeat sizes, a long repeat seen in the large fragments and a small repeat seen in the small fragments. The two repeats hardly overlap, except in a narrow transition zone which is at a different fragment size in the BR 2.2 and the BR 2.1 gene. The sizes of the large repeats fit the repeat of the underlying DNA sequence. The short repeats are between 170 and 180 bp, and after H1 depletion the short repeat in the BR 2.2 gene is 160 bp. Our most favoured interpretation of these data is that in intact chromatin the nucleosomes in the BR genes are phased with respect to the repeating DNA sequence, whereas micrococcus nuclease digestion leads to loss of a nucleosome-positioning constraint and hence to rearrangement of the nucleosomes. Our results imply a possible artefact of nuclease digestion of chromatin, which has to be taken into account in mapping nucleosome positions.     

Host-specific regulation of nodulation genes in Rhizobium is mediated by a plant-signal, interacting with the nodD gene product

We have identified a nodD gene from the wide host-range Rhizobium strain MPIK3030 (termed nodD1) which is essential for nodulation on Macroptilium atropurpureum (siratro). Experiments with nodA–lacZ gene fusions demonstrate that the MPIK3030 nodD1 regulates expression of the nodABC genes. Additionally, we used nodC–lacZ fusions of Rhizobium meliloti to show that the MPIK3030 nodD1 gene induces expression of these fusions by interacting with plant factors from siratro and from the non-host Medicago sativa (alfalfa). The R. meliloti nodD genes, however, only interact with alfalfa exudate. In line with these results, no complementation of MPIK3030 nodD1 mutants could be obtained on siratro with the R. meliloti nodD genes, while the MPIK3030 nodD1 can complement nodD mutants of R. meliloti on alfalfa. Furthermore, R. meliloti transconjugants harbouring the MPIK3030 nodD1 efficiently nodulate the illegitimate host siratro. When compared with other nodD sequences, the amino acid sequence of the MPIK3030 nodD1 shows a conserved aminoterminus, whereas the carboxy-terminus of the putative gene product diverges considerably. Studies on a chimeric MPIK3030/R. meliloti nodD gene indicates that the carboxy-terminal region is responsible for the interaction with plant factor(s) and may have evolved in different rhizobia specifically to interact with plant–host factors.     

Stoichiometric differences in DNA molecules containing the atpA gene suggest mechanisms for the generation of mitochondrial genome diversity in maize

Four genomic arrangements of the maize mitochondrial atpA gene (encoding the α subunit of the F₁ ATPase), have been characterized. Most N (fertile) and S (male-sterile) cytoplasms contain two atpA arrangements of equal abundance. Prolonged exposure of blots of maize mitochondrial DNA probed with atpA-specific sequences show that cytoplasms previously reported to lack one of the atpA arrangements do contain the second arrangement but at low levels. Similarly, restriction fragments containing the atpA gene previously thought unique to male-sterile S and T cytoplasms are present in low abundance in fertile cytoplasms. These observations suggest that fertile and male-sterile cytoplasms of maize may be more closely related than previously thought, and suggest possible mechanisms to explain the observed mitochondrial genome diversity.