Assembly of transcriptionally active chromatin in Xenopus oocytes requires specific DNA binding factors

Active minichromosomes assembled on injected 5S RNA gene clones are stable in Xenopus oocytes; endogenous 5S DNA specific factor(s) are required for their assembly. When somatic-type and oocyte-type 5S RNA gene clones are coinjected, the somatic genes are assembled into active minichromosomes, while most of the oocyte genes are assembled into inactive ones. The differential 5S RNA gene expression, which mimics that in somatic cells, appears to result from titration of 5S DNA specific factor(s) by the competing somatic 5S DNA, followed by histone mediated assembly of inactive chromatin on the oocyte 5S DNA. Stable minichromosomes are also assembled on a cloned histone H4 gene; again, intragenic DNA rearrangements affect the efficiency of assembly of active chromatin and differential gene expression occurs after coinjection of two or more H4 DNA constructs. We suggest that the H4 DNA molecules also compete for limiting quantities of specific DNA binding factor(s) required for the assembly of active H4 gene chromatin.     

The un body: a possible structure for transcriptionally inactivated chromatin subunits

The Weibull distribution is increasingly finding application in the biological sciences, notably in forestry, where it has given good fits to tree-diameter frequency distribution. Interest among foresters is currently focused on improving the interpretation for the two parameters of this distribution, resulting in better understanding of forest stand growth.This paper presents a mathematical derivation of the Weibull distribution based on a generalization of the broken stick model used in ecology for species-abundance curves. This derivation suggests that the inverse of one parameter can be interpreted as an index of non-randomness and that the other parameter is inversely proportional to total frequency in an observed frequency distribution.