MOLECULAR STUDY ON CYTOTOXIN OF PSUDO-MONAS AERUGINOSA AND CYTOTOXIN-CONVERTING PHAGE

1.噬菌体PHICTX的分子分析：（1）确定了cos位点的结构。（2）阐明了attB位点“核心”区域的结构。结果表明，PHICTX的attB基因位于染色体上丝氨酸-tRNA基因的3'端，即铜绿假单胞菌PAO遗传图谱的42'-45 '端，该区域与大肠杆菌相应区域的核苷酸序列有很高的同源性。（3）在att-cos-ctx区域存在许多“重复序列”、“重复DNA”和IHF结合序列。（4）PHICTX的int和xis基因位于attP附近。2. PHICTX与R（Rod shaped）Pyocin的关系：（1）根据PHICTX的免疫学特性和DNA序列的同源性，确定PHICTX是一种与R（Rod shaped）Pyocin相关的噬菌体。（2）PHICTX的受体位于LPS的外核心区，其免疫原性仅限于有限的血清型。（3）在所检测的绿脓菌素相关菌株中，PS21被证实具有ctx。（4）确定了不含ctx但与PHICTX基因组同源的绿脓菌素相关基因的分布。3.在其他细菌中寻找ctx相关基因：用ctx的DNA作为探针，通过Southern试验对数百株不同细菌进行了研究，但没有基因与探针杂交。

1.Molecular analysis of phage PHICTX : (1)Structure of cos site has been determined. (2)Structure of the "core" region of the attB site has been clarified. The attB of the PHICTX was found to be the 3' region of serine-tRNA gene on chromosome which was lcated 42'-45' region of genetic map of P.aeruginosa PAO.The region has a significant homology, in its nucleotide sequence, with the corresponding region of E.coli. (3)Existence of many "repeated sequences", "bent-DNA" and the binding sequence for IHF has become evident in the att-cos-ctx region. (4)The two genes, which were supposed to be the int and xis, respectively, of PHICTX have been found near the attP.2.Relationship between PHICTX and R(Rod shaped)Pyocins : (1)PHICTX has been identified as an R Pyocin-related phage based on immunological property and homology of DNA sequences. (2)Receptor of PHICTX has been identified as the outer-core region of LPS.Infectivity of PHICTX confined only a restricted serotypes. (3)Among the R pyocin-related phages tested, PS21 was proved to have ctx. (4)Distribution of the R pyocin-related phages without ctx but have homology with PHICTX genome was confirmed. 3.Search for the genes related to ctx in other bacteria : This has been done for several hundred strains of various bacterial species using DNA of ctx as the probe by Southern test but none of gene hybridized with the probe.