PubMed Health⌕ Search

Biomedical subjects

A Kazantsev

Publications and source records attributed to A Kazantsev.

9 recordsLinked to original sources
PubMed1998

Role of mouse cryptochrome blue-light photoreceptor in circadian photoresponses.

Cryptochromes are photoactive pigments in the eye that have been proposed to function as circadian photopigments. Mice lacking the cryptochrome 2 blue-light photoreceptor gene (mCry2) were tested for circadian clock-related functions. The mutant mice had a lower sensitivity to acute light induction of mPer1 in the suprachiasmatic nucleus (SCN) but exhibited normal circadian oscillations of mPer1 and mCry1 messenger RNA in the SCN. Behaviorally, the mutants had an intrinsic circadian period about 1 hour longer than normal and exhibited high-amplitude phase shifts in response to light pulses administered at circadian time 17. These data are consistent with the hypothesis that CRY2 protein modulates circadian responses in mice and suggest that cryptochromes have a role in circadian photoreception in mammals.

Animals↗
PubMed1998

Generation and characterization of an immortal cell line of xeroderma pigmentosum group E.

Xeroderma pigmentosum group E (XP-E) fibroblasts (XP95TO) were transformed with pSV3neo. Selection in medium containing G418 yielded 14 clones with extended life span. Following crisis, one clone was recovered that behaved in culture as an immortal cell line and was named XPET6/1. Expression of the SV40 large T antigen gene (Tag) and increased level of p53 were demonstrated by western analyses. Fingerprinting with 14 polymorphic microsatellite genetic markers confirmed that XPET6/1 originated from the parental strain XP95TO. XPET6/1 retained the sensitivity to killing by UV observed with the parental strain. Cell-free extracts from the immortal or the parental XP-E cells were deficient in excision, compared to extracts from HeLa or extracts from Tag-transformed XP variant fibroblasts. Complementation of XP-E extracts with XP-A, XP-D or XP-G extracts restored nucleotide excision activity to normal levels. XPET6/1 could prove a useful cell line for cloning of the XPE gene by functional complementation.

Cell Culture Techniques↗
PubMed1996

Putative human blue-light photoreceptors hCRY1 and hCRY2 are flavoproteins.

Recently, a human cDNA clone with high sequence homology to the photolyase/blue-light photoreceptor family was identified. The putative protein encoded by this gene exhibited a strikingly high (48% identity) degree of homology to the Drosophila melanogaster (6-4) photolyase [Todo et al. (1996) Science 272, 109-112]. We have now identified a second human gene whose amino acid sequence displays 73% identity to the first one and have named the two genes CRY1 and CRY2, respectively. The corresponding proteins hCRY1 and hCRY2 were purified and characterized as maltose-binding fusion proteins. Similar to other members of the photolyase/blue-light photoreceptor family, both proteins were found to contain FAD and a pterin cofactor. Like the plant blue-light photoreceptors, both hCRY1 and hCRY2 lacked photolyase activity on the cyclobutane pyrimidine dimer and the (6-4) photoproduct. We conclude that these newly discovered members of the photolyase/photoreceptor family are not photolyases and instead may function as blue-light photoreceptors in humans.

Amino Acid Sequence↗
PubMed1996

Functional complementation of xeroderma pigmentosum complementation group E by replication protein A in an in vitro system.

Xeroderma pigmentosum (XP) is caused by a defect in nucleotide excision repair. Patients in the complementation group E (XP-E) have the mildest form of the disease and the highest level of residual repair activity. About 20% of the cell strains derived from XP-E patients lack a damaged DNA-binding protein (DDB) activity that binds to ultraviolet-induced (6-4) photoproducts with high affinity. We report here that cell-free extracts prepared from XP-E cell strains that either lacked or contained DDB activity were severely defective in excising DNA damage including (6-4) photoproducts. However, this excision activity defect was not restored by addition of purified DDB that, in fact, inhibited removal of (6-4) photoproducts by the human excision nuclease reconstituted from purified proteins. Extensive purification of correcting activity from HeLa cells revealed that the correcting activity is inseparable from the human replication/repair protein A [RPA (also known as human single stranded DNA binding protein, HSSB)]. Indeed, supplementing XP-E extracts with recombinant human RPA purified from Escherichia coli restored excision activity. However, no mutation was found in the genes encoding the three subunits of RPA in an XP-E (DDB-) cell line. It is concluded that RPA functionally complements XP-E extracts in vitro, but it is not genetically altered in XP-E patients.

Base Sequence↗
PubMed1994

Substrate spectrum of human excinuclease: repair of abasic sites, methylated bases, mismatches, and bulky adducts.

Nucleotide-excision repair is the repair system for removing bulky lesions from DNA. Humans deficient in this repair pathway suffer from xeroderma pigmentosum (XP), a disease characterized by photodermatoses, including skin cancers. At the cellular level, XP patients fail to remove cyclobutane pyrimidine dimers and pyrimidine(6-4)pyrimidone photoproducts induced by UV light, as well as other bulky DNA lesions caused by various genotoxic agents. XP cells are not particularly sensitive to ionizing radiation or to alkylating agents that cause mostly nonbulky DNA lesions. Therefore, it has generally been assumed that the human nucleotide-excision repair enzyme (excinuclease) is specific for bulky adducts. To determine the substrate range of human excinuclease we used the highly sensitive excision assay and tested bulky adducts, synthetic apurinic/apyrimidinic sites, N6-methyladenine, O6-methylguanine, and mismatches as potential substrates. We found that all of these "lesions" were removed by human excinuclease, although with vastly different efficiencies.

Animals↗
PubMed1992

Confirmation of genetic heterogeneity in limb-girdle muscular dystrophy: linkage of an autosomal dominant form to chromosome 5q.

Limb-girdle muscular dystrophy (LGMD) is a clinically and genetically heterogenous group of disorders, with both recessive and dominant forms reported. Recently, a series of recessive LGMD families were linked to chromosome 15q. We report herein the results of our linkage studies in a previously reported large autosomal dominant family. The LGMD gene in this family was localized to chromosome 5q22.3-31.3 by using a series of CA(n) microsatellite repeat markers. Linkage to 15q was excluded. These findings confirm genetic heterogeneity in this clinically diverse syndrome.

Cell Line, Transformed↗