Complete inhibition of Cdk/cyclin by one molecule of p21 (super Cip1)

Article Abstract:

Using various techniques, among them analytical ultracentrifugation of purified p21/cyclinA/Cdk2 complexes, it has been clearly shown that just one p21 molecule is adequate to bring kinase inhibition. Also p21-saturated complexes have been shown to have only one inhibitor molecule bound in a stable way. Phosphorylated forms of p21 are efficient cyclin-dependent kinase (Cdk) activities inhibitors. The degree to which Cdk is inactivated by p21 depends on the fraction of kinase complexed with the inhibitor, not by stoichiometry of inhibitor bonded to the kinase or by phosphorylation state of the Cdk inhibitor. Cdks control cell-cycle phase transitions. Cdk inhibitors are vital to the regulation of these kinase activities. The Cdk inhibitors are proteins induced in response to various antiproliferative signals. They can oscillate during cell-cycle progression and lead to Cdk inactivation.

Germany, Protein kinases

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c-myc null cells misregulate cad and gadd45 but not other proposed c-Myc targets

Article Abstract:

Expression of almost all potential c-Myc target genes is not changed in cells having a homozygous null deletion of c-myc. It has been shown that a loss-of-function approach is essential for evaluating possible c-Myc target genes. An exception worth noting is the cad gene, one that has cut down log phase expression and serum induction in c-myc null cells. Another is the growth arrest gene, gadd45. Repression is reversed by knockout of c-myc. As a result it is seen that gadd45 and cad are the only potential targets of c-Myc that perhaps contribute to the dramatic slow growth phenotype of c-myc null cells.

Cellular signal transduction

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Negative control of replication initiation by a novel chromosomal locus exhibiting exceptional affinity for Escherichia coli DnaA protein

Article Abstract:

Replication initiation is negatively controlled by a novel chromosomal locus. That locus has remarkable affinity for Escherichia coli DnaA protein. Replication of the E. coli chromosome is started at oriC, a unique site. Initiation that is concurrent occurs at all oriC sites in a cell only once in any cell cycle. A mechanism that ensures cyclic initiation operates through the chromosomal site, datA, a 1-kb segment located at 94.7 min on the genetic map. The map titrates exceptionally large amounts of the bacterial initiator protein, DnaA.

Escherichia coli, Cellular control mechanisms, Cell regulation, Chromosome replication, Chromosomal proteins

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