The Mutation of the Suppressor of Underreplication Gene Does Not Affect the Replication Fork Rate in the Drosophila melanogaster Salivary Gland Polytene Chromosomes

摘要

Underreplication of heterochromatin regions of polytene chromosomes of D. melanogaster salivary glands is under the control of the Suppressor of Underreplication (SuUR) gene. We have tested the hypothesis whether SuUR can directly affect the rate of replication fork progression. The replication rate was analyzed by molecular combing, which was adapted for studying DNA replication in isolated organs of Drosophila. The results showed that the mean rate of replication fork progression in chromosomes of salivary glands of the wild type Drosophila larvae and the SuUR mutants do not differ significantly. Analysis of the replication rate in a single intercalary heterochromatin region containing histone gene cluster also revealed no significant differences between the SuUR mutants and the wild type larvae. The results of this study indicate that the SuUR mutation does not directly affect the rate of replication fork progression. Possible molecular mechanisms of the effect of this mutation on replication are discussed.