No abstract

The chromatin subunit or nucleosome structure in the fertilized embryo of the sea urchin Strongylocentrotus purpuratus has been investigated during early stages of growth when the translation of mRNA for histone variants of HI, H2A, and H2B is markedly changing. It is shown that nucleosomes exist prior to differentiation, in cells which are "totipotent". We have found that micrococcal nuclease derived monomer and multimeric nucleosomes can also be isolated from each stage of development, beginning with the two-cell embryo. Basic proteins in the nucleosome fractions have been analyzed directly by employing a new technique developed in our laboratory: protamine release of chromosomal proteins into Triton-acid-urea mini gels [Shaw, B. R., & Richards, R. G. (1979) NATO Adv. Study Inst. Ser., Ser. A 21a, 125-136], These studies indicate that cleavage-stage proteins are nucleosomal proteins. Likewise, the a-type histone H2A variant and each of the putative late stage f), y, and 8 H2AIjittle is known as to how variations in histone subtypes other than HI affect the structure of chromatin. Multiple forms of histones H2A, H2B, and H3, which differ by one or several amino acids in their primary sequence, have been identified in a number of organisms (

Random amplified polymorphic DNA analysis of blood samples from eight African parrot species was performed to study the genetic relationship within the genus Poicephalus and among Poicephalus and the two other main African parrot genuses, Agapornis and Psittacus. To this end, DNA from six Poicephalus species, one species, of the Agapornis group and the single Psittacus species was analysed. The amplification pattern was then converted into a binary matrix and scored by the unweighted pair-group method algorithm. The resulting dendrogram showed a neat separation of all the Poicephalus on one side, from Psittacus-Agapornis on the other side. Among the six analysed species of Poicephalus, two larger clusters occurred, one containing four species belonging to the P. meyeri superspecies and the other one containing the two species pertaining to the P. robustus superspecies. The larger one of these is further subdivided in two smaller clusters, each one containing two species, that is P. meyeri-P. cryptoxanthus and P. senegalus-P. rufiventris, respectively. These results are consistent with the hypothesis that the genus Poicephalus is a natural assemblage that, after undergoing a very early separation from Psittacus and Agapornis, was subsequently affected by a number of discrete speciation events, especially during episodes of aridity resulting in fragmentation of forest habitats.

A typical nucleosomal pattern is not detected by electrophoretic analysis of sea urchin mature egg chromatin, following digestion with micrococcal nuclease. Moreover, at least 80% of the egg nuclear DNA is resistant to nuclease attack. These unusual features of unfertilized egg chromatin, not shared by oocytes or sperms, are discussed in view of the unique properties and fate of mature female germ cells.

No abstract