Cheng Y, Kaiser D
Department of Biochemistry, Stanford University, California 94305.
J Bacteriol. 1989 Jul;171(7):3719-26. doi: 10.1128/jb.171.7.3719-3726.1989.
dsg mutants of Myxococcus xanthus are conditionally defective in fruiting body development, including sporulation. Unable to develop on their own, these mutants can assemble fruiting bodies with spores if they are mixed with wild-type cells. To elucidate the developmental defect in dsg mutants by close comparison with wild type, such mutants have been backcrossed by transduction, using a closely linked insertion of transposon Tn5 for selection. Backcrossed dsg mutants form aggregates that are larger, less compact, and less symmetrical than dsg+ fruiting bodies. Also, the starvation-induced sporulation in dsg aggregates is delayed and reduced. However, dsg mutants can be induced by glycerol or dimethyl sulfoxide to sporulate at levels approaching those of wild type. dsg mutants may thus have a primary defect early in development which diminishes their capacity to aggregate and which indirectly decreases the number of fruiting body spores. The linked insertion of Tn5 also facilitated cloning the dsg gene. The cloned dsg+ allele was shown to be dominant to both the dsg-429 and dsg-439 alleles, and both mutant alleles were shown to belong to the same genetic complementation group. Subcloning of restriction fragments, deletions, and insertions of transposon Tn5 agree in locating the dsg gene to an 850-base-pair segment of the cloned region.
黄色粘球菌的dsg突变体在子实体发育（包括孢子形成）方面存在条件性缺陷。这些突变体无法自行发育，但如果与野生型细胞混合，它们可以组装带有孢子的子实体。为了通过与野生型进行密切比较来阐明dsg突变体的发育缺陷，已使用转座子Tn5的紧密连锁插入进行选择，通过转导对这些突变体进行回交。回交后的dsg突变体形成的聚集体比dsg+子实体更大、更松散且对称性更低。此外，dsg聚集体中饥饿诱导的孢子形成延迟且减少。然而，甘油或二甲基亚砜可诱导dsg突变体以接近野生型的水平形成孢子。因此，dsg突变体可能在发育早期存在主要缺陷，这削弱了它们聚集的能力，并间接减少了子实体孢子的数量。Tn5的连锁插入也有助于克隆dsg基因。克隆的dsg+等位基因对dsg - 429和dsg - 439等位基因均呈显性，且两个突变等位基因均属于同一遗传互补群。限制片段的亚克隆、缺失和转座子Tn5的插入均一致地将dsg基因定位到克隆区域的一个850个碱基对的片段上。
