Nuclear calmodulin/62 kDa calmodulin-binding protein complexes in interphasic and mitotic cells.
We report here that a 62 kDa calmodulin-binding protein (p62), recently identified in the nucleus of rat hepatocytes, neurons and glial cells, consists of four polypeptides showing pI values between 5.9 and 6.1. By using a DNA-binding overlay assay we found that the two most basic of the p62 polypeptides bind both single- and double-stranded DNA. The intranuclear distribution of calmodulin and p62 was analysed in hepatocytes and astrocyte precursor cells, and in proliferating and differentiated astrocytes in primary cultures by immunogold-labeling methods. In non-dividing cells nuclear calmodulin was mostly localized in heterochromatin although it was also present in euchromatin and nucleoli. A similar pattern was observed for p62, with the difference that it was not located in nucleoli. p62/calmodulin complexes, mainly located over heterochromatin domains were also observed in interphasic cells. These complexes remained associated with the nuclear matrix after in situ sequential extraction with nucleases and high-salt containing buffers. In dividing cells, both calmodulin and p62 were found distributed over all the mitotic chromosomes but the p62/calmodulin aggregates were disrupted. These results suggest a role for calmodulin and p62 in the condensation of the chromatin.
Portolés
M
M
Centro de Investigación, Hospital LA FE, Valencia, Spain.
Faura
M
M
Renau-Piqueras
J
J
Iborra
F J
FJ
Saez
R
R
Guerri
C
C
Serratosa
J
J
Rius
E
E
Bachs
O
O
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D002466:Cell Nucleolus / Q000737:chemistry; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D002843:Chromatin / Q000737:chemistry; D004247:DNA / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D007399:Interphase / Q000502:physiology; D008099:Liver / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D008938:Mitosis / Q000502:physiology; D011485:Protein Binding; D051381:Rats
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D002843:Chromatin; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D004247:DNA