The N-Terminal Domain of the Drosophila Retinoblastoma Protein Rbf1 Interacts with ORC and Associates with Chromatin in an E2F Independent Manner

The retinoblastoma (Rb) tumor suppressor protein can function as a DNA replication inhibitor as well as a transcription factor. Regulation of DNA replication may occur through interaction of Rb with the origin recognition complex (ORC).We characterized the interaction of Drosophila Rb, Rbf1, with ORC. Using expression of proteins in Drosophila S2 cells, we found that an N-terminal Rbf1 fragment (amino acids 1-345) is sufficient for Rbf1 association with ORC but does not bind to dE2F1. We also found that the C-terminal half of Rbf1 (amino acids 345-845) interacts with ORC. We observed that the amino-terminal domain of Rbf1 localizes to chromatin in vivo and associates with chromosomal regions implicated in replication initiation, including colocalization with Orc2 and acetylated histone H4.Our results suggest that Rbf1 can associate with ORC and chromatin through domains independent of the E2F binding site. We infer that Rbf1 may play a role in regulating replication directly through its association with ORC and/or chromatin factors other than E2F. Our data suggest an important role for retinoblastoma family proteins in cell proliferation and tumor suppression through interaction with the replication initiation machinery

Molecular cytogenetic organization of polytene chromosomes

The results of the works carried out in the Laboratory of Molecular Cytogenetics (Institute of Cytology and Genetics of Siberian Branch of the RAS, Novosibirsk) devoted to the molecular genetic analysis of main units of polytene chromosomes,*(1) bands, interbands, and puffs, as well as intercalary and pericentric heterochromatin,*(2) are summarized. The results are discussed in terms of the dynamic model of organization of polytene chromosomes

Identification of bacterial biofilm and the Staphylococcus aureus derived protease, staphopain, on the skin surface of patients with atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by an impaired epidermal barrier, dysregulation of innate and adaptive immunity, and a high susceptibility to bacterial colonization and infection. In the present study, bacterial biofilm was visualized by electron microscopy at the surface of AD skin. Correspondingly, Staphylococcus aureus (S. aureus) isolates from lesional skin of patients with AD, produced a substantial amount of biofilm in vitro. S. aureus biofilms showed less susceptibility to killing by the antimicrobial peptide LL-37 when compared with results obtained using planktonic cells. Confocal microscopy analysis showed that LL-37 binds to the S. aureus biofilms. Immuno-gold staining of S. aureus biofilm of AD skin detected the S. aureus derived protease staphopain adjacent to the bacteria. In vitro, staphopain B degraded LL-37 into shorter peptide fragments. Further, LL-37 significantly inhibited S. aureus biofilm formation, but no such effects were observed for the degradation products. The data presented here provide novel information on staphopains present in S. aureus biofilms in vivo, and illustrate the complex interplay between biofilm and LL-37 in skin of AD patients, possibly leading to a disturbed host defense, which facilitates bacterial persistence