Tsang A, Bonfils C, Czaika G, Shtevi A, Grant C
Department of Biology, Concordia University, Montreal, Quebec, Canada.
Biochim Biophys Acta. 1996 Nov 11;1309(1-2):100-8. doi: 10.1016/s0167-4781(96)00109-1.
We have isolated the gene. rnrB, that encodes the ribonucleotide reductase small subunit of Dictyostelium discoideum. The deduced amino acid sequence of rnrB exhibits about 60% sequence identity with its homologues in other eukaryotes. As demonstrated by RNA blot analysis the rnrB transcript is detected in growing cells and decreases dramatically at the onset of development. The rnrB transcript reappears after the cells have formed multicellular aggregates. To further examine the pattern of expression, we have fused the rnrB promoter and part of its coding sequence to lacZ. The transgenic strain bearing such a reporter construct expresses the fusion gene with a biphasic profile, which is indistinguishable from that of the endogenous rnrB. The multicellular aggregates of Dictyostelium are differentiated along the anterior-posterior axis. Cells in the anterior give rise to the stalk of the fruiting body while cells in the posterior are precursors of spores. Results from histochemical staining show that beta-galactosidase activity is detected exclusively in the posterior two-thirds of the aggregates. These data suggest that rnrB is expressed in prespore cells during postaggregative development and in vegetative cells.
我们已经分离出了编码盘基网柄菌核糖核苷酸还原酶小亚基的基因rnrB。rnrB推导的氨基酸序列与其在其他真核生物中的同源物具有约60%的序列同一性。RNA印迹分析表明，rnrB转录本在生长细胞中被检测到，在发育开始时急剧下降。在细胞形成多细胞聚集体后，rnrB转录本重新出现。为了进一步研究表达模式，我们将rnrB启动子及其部分编码序列与lacZ融合。携带这种报告构建体的转基因菌株以双相模式表达融合基因，这与内源性rnrB的表达模式无法区分。盘基网柄菌的多细胞聚集体沿前后轴分化。前部的细胞形成子实体的柄，而后部的细胞是孢子的前体。组织化学染色结果表明，β-半乳糖苷酶活性仅在聚集体后部的三分之二区域被检测到。这些数据表明，rnrB在聚集后发育过程中的前孢子细胞以及营养细胞中表达。
