Is O-1(2) alone sufficient for DNA cleavage? Possible involvement of paramagnetic intermediates

It is proposed that singlet dioxygen reacting with guanosine or deoxyguanosine part of nucleotides does not, by itself, cause DNA cleavage. The strand break originates at the endoperoxide stage whenever this link evolves into a O-centered radical. The O-centered radical is then in a good spatial position to abstract an hydrogen intramolecularly from the ribose or desoxyribose part of the nucleotide. The carbon centered radical thus formed on the sugar part may lead to strand break either by a p-scission mechanism or by an homolytically induced solvolysis. High pH could also induce cleavage after the endoperoxide stage via a base catalyzed ring chain protomerism.

Sex-specific organisation of middle repetitive DNA sequences in the mealybug Planococcus lilacinus

Differential organisation of homologous chromosomes is related to both sex determination and genomic imprinting in coccid insects, the mealybugs. We report here the identification of two middle repetitive sequences that are differentially organised between the two sexes and also within the same diploid nucleus. These two sequences form a part of the male-specific nuclease-resistant chromatin (NRC) fraction of a mealybug Planococcus lilacinus. To understand the phenomenon of differential organisation we have analysed the components of NRC by cloning the DNA sequences present, deciphering their primary sequence, nucleosomal organisation, genomic distribution and cytological localisation, Our observations suggest that the middle repetitive sequences within NRC are functionally significant and we discuss their probable involvement in male-specific chromatin organisation.