A MALE-SPECIFIC NUCLEASE-RESISTANT CHROMATIN FRACTION IN THE MEALYBUGPLANOCOCCUS-LILACINUS

In mealybugs, chromatin condensation is related to both genomic imprin ting and sex determination. The paternal chromosomal complement is con densed and genetically inactive in sons but not in daughters. During a study of chromatin organization in Planococcus lilacinus, digestion w ith micrococcal nuclease showed that 3% to 5% of the male genome is re sistant to the enzyme. This Nuclease Resistant Chromatin (NRC) apparen tly has a nucleosomal organization. Southern hybridization of genomic DNA suggests that NRC sequences are present in both sexes and occur th roughout the genome. Cloned NRC DNA is A+T-rich with stretches of aden ines similar to those present in mouse alpha-satellite sequences. NRC DNA also contains sequence motifs that are typically associated with t he nuclear matrix. Salt-fractionation experiments showed that NRC sequ ences are matrix associated. These observations are discussed in relat ion to the unusual cytological features of mealybug chromosomes, inclu ding the possible existence of multiple centres of inactivation.