Waldo R H, Popham P L, Romero-Arroyo C E, Mothershed E A, Lee K K, Krause D C
Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
J Bacteriol. 1999 Aug;181(16):4978-85. doi: 10.1128/JB.181.16.4978-4985.1999.
Mycoplasma pneumoniae adherence to host cells is a multifactorial process that requires the cytadhesin P1 and additional accessory proteins. The hmw gene cluster consists of the genes p30, hmw3, and hmw1, the products of which are known to be essential for cytadherence, the rpsD gene, and six open reading frames of unknown function. Putative transcriptional terminators flank this locus, raising the possibility that these genes are expressed as a single transcriptional unit. However, S1 nuclease protection and primer extension experiments identified probable transcriptional start sites upstream of the p32, p21, p50, and rpsD genes. Each was preceded at the appropriate spacing by the -10-like sequence TTAAAATT, but the -35 regions were not conserved. Analysis of the M. pneumoniae genome sequence indicated that this promoter-like sequence is found upstream of only a limited number of open reading frames, including the genes for P65 and P200, which are structurally related to HMW1 and HMW3. Promoter deletion studies demonstrated that the promoter-like region upstream of p21 was necessary for the expression of p30 and an hmw3-cat fusion in M. pneumoniae, while deletion of the promoter-like region upstream of p32 had no apparent effect. Analysis by reverse transcription-PCR confirmed transcriptional linkage of all the open reading frames in the hmw gene cluster. Taken together, these findings suggest that the genes of this locus constitute an operon expressed from overlapping transcripts.
肺炎支原体对宿主细胞的黏附是一个多因素过程，需要细胞黏附素P1和其他辅助蛋白。hmw基因簇由p30、hmw3和hmw1基因组成，已知其产物对细胞黏附至关重要，还有rpsD基因以及六个功能未知的开放阅读框。推测的转录终止子位于该基因座两侧，这增加了这些基因作为单个转录单元表达的可能性。然而，S1核酸酶保护和引物延伸实验确定了p32、p21、p50和rpsD基因上游可能的转录起始位点。每个转录起始位点之前都有适当间隔的类似-10序列TTAAAATT，但-35区域并不保守。对肺炎支原体基因组序列的分析表明，这种类似启动子的序列仅在有限数量的开放阅读框上游发现，包括与HMW1和HMW3结构相关的P65和P200基因。启动子缺失研究表明，p21上游的类似启动子区域对于肺炎支原体中p30和hmw3-cat融合蛋白的表达是必需的，而p32上游的类似启动子区域缺失没有明显影响。逆转录-PCR分析证实了hmw基因簇中所有开放阅读框的转录连锁。综上所述，这些发现表明该基因座的基因构成了一个由重叠转录本表达的操纵子。
