Zhimulev I F, Belyaeva E S, Bolshakov V N, Mal'ceva N I
Institute of Cytology and Genetics, Novosibirsk, USSR.
Chromosoma. 1989 Nov;98(5):378-87. doi: 10.1007/BF00292391.
The behaviour of IH (intercalary heterochromatin) regions of Drosophila melanogaster polytene chromosomes was compared with that of euchromatin condensed as a result of position-effect variegation. Normally replicating regions, when subject to such an effect, were found to become among the last regions in the genome to replicate. It is shown that the factors which enhance position effect (low temperature, the removal of the Y chromosome, genetic enhancers of position effect) increase the weak point frequency in the IH, i.e. enhance DNA underreplication in these regions. We suggest that the similarity in the properties of IH, CH (centromeric heterochromatin) and the dense blocks induced by position effect is due to strong genetic inactivation and supercondensation caused by specific proteins in early development. The primary DNA structure is not likely to play a key role in this process.
将黑腹果蝇多线染色体的居间异染色质（IH）区域的行为与因位置效应斑驳而浓缩的常染色质的行为进行了比较。正常复制区域在受到这种效应影响时，被发现成为基因组中最后复制的区域之一。结果表明，增强位置效应的因素（低温、Y染色体的去除、位置效应的遗传增强子）会增加IH中的弱点频率，即增强这些区域的DNA复制不足。我们认为，IH、着丝粒异染色质（CH）以及由位置效应诱导的致密区域在性质上的相似性是由于早期发育中特定蛋白质引起的强烈基因失活和超浓缩。在此过程中，DNA一级结构不太可能起关键作用。
