Biomedical subjects

Y Katan-Khaykovich

Publications and source records attributed to Y Katan-Khaykovich.

3 recordsLinked to original sources

PubMed2001

Nuclear import and DNA-binding activity of RFX1. Evidence for an autoinhibitory mechanism.

RFX1 binds and regulates the enhancers of a number of viruses and cellular genes. RFX1 belongs to the evolutionarily conserved RFX protein family that shares a DNA-binding domain and a conserved C-terminal region. In RFX1 this conserved region mediates dimerization, and is followed by a unique C-terminal tail, containing a highly acidic stretch. In HL-60 cells nuclear translocation of RFX1 is regulated by protein kinase C with unknown mechanisms. By confocal fluorescence microscopy, we have identified a nonclassical nuclear localization signal (NLS) at the extreme C-terminus. The adjacent 'acidic region', which showed no independent NLS activity, potentiated the function of the NLS. Subcellular fractionation showed that the tight association of RFX1 with the nucleus is mediated by its DNA-binding domain and enhanced by the dimerization domain. In contrast, the acidic region inhibited nuclear association, by down-regulating the DNA-binding activity of RFX1. These data suggest an autoinhibitory interaction, which may regulate the function of RFX1 at the level of DNA binding. The C-terminal tail thus constitutes a composite localization domain, which on the one hand mediates nuclear import of RFX1, and on the other hand inhibits its association with the nucleus and binding to DNA. The participation of the acidic region in both activities suggests a mechanism by which the nuclear import and DNA-binding activity of RFX1 may be coordinately regulated by phosphorylation by kinases such as PKC.

Animals↗

PubMed1999

The dimerization/repression domain of RFX1 is related to a conserved region of its yeast homologues Crt1 and Sak1: a new function for an ancient motif.

The RFX protein family includes members from yeast to humans, which function in various biological systems, and share a DNA-binding domain and a conserved C-terminal region. In the human transcription regulator RFX1, the conserved C terminus is an independent functional domain, which mediates dimerization and transcriptional repression. This dimerization domain has a unique ability to mediate the formation of two alternative homodimeric DNA-protein complexes, the upper of which has been linked to repression. Here, we localize the complex formation capacity to several different RFX1 C-terminal subregions, each of which can function independently to generate the upper complex and repress transcription, thus correlating complex formation with repression. To gain an evolutionary perspective, we have examined whether the different properties of the RFX1 C terminus exist in the two yeast RFX proteins, which are involved in signaling pathways. Replacement of the RFX1 C terminus with those of Sak1 and Crt1, its orthologues from Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively, and analysis of fusions with the Gal4 DNA-binding domain, revealed that the ability to generate the two alternative complexes is conserved in the RFX family, from S. cerevisiae to man. While sharing this unique biochemical property, the three C termini differed from each other in their ability to mediate dimerization and transcriptional repression. In both functions, RFX1, Sak1, and Crt1 showed high capacity, moderate capacity, and no capacity, respectively. This comparative analysis of the RFX proteins, representing different evolutionary stages, suggests a gradual development of the conserved C terminus, from the appearance of the ancestral motif (Crt1), to the later acquisition of the dimerization/repression functions (Sak1), and finally to the enhancement of these functions to generate a domain mediating highly stable protein-protein interactions and potent transcriptional repression (RFX1).

Amino Acid Sequence↗

PubMed1998

RFX1, a single DNA-binding protein with a split dimerization domain, generates alternative complexes.

The transcription of various viral and cellular genes is regulated by palindromic and nonpalindromic DNA sites resembling the EP element of the hepatitis B virus enhancer, which generate similar DNA-protein complexes. The upper EP complex contains homodimers of the transcription regulator RFX1. We show that RFX1 possesses a split, extended dimerization domain composed of several evolutionarily conserved boxes, one of which was previously shown to mediate dimerization. Such an unusually long and complex dimerization domain could potentially serve for generating multiple complexes. In addition to the previously characterized complex, RFX1 generated a novel DNA-protein complex of extremely low mobility, formed only with palindromic DNA sites. Different deletions within the dimerization domain altered the relative abundance of the two complexes, suggesting an interplay between them. Formation of the low mobility complex correlated with transcriptional repression, in that both activities were mediated by several portions of the conserved region. Our results propose a mechanism by which the extended dimerization domain mediates the formation of alternative homodimeric complexes, which differ in the nature of the intersubunit interaction. By participating in different types of interactions, this domain may regulate the relative abundance of the different complexes, thus affecting transcriptional activity.

Alternative Splicing↗