Search PubMed⌕ Search

Biomedical subjects

S Maiti

Publications and source records attributed to S Maiti.

50 records · Page 3Linked to original sources
PubMed1996

The Pem homeobox gene: rapid evolution of the homeodomain, X chromosomal localization, and expression in reproductive tissue.

A hallmark of homeobox genes is their high degree of sequence conservation in distantly related species. Here, we report the chromosomal localization, sequence, and expression pattern of an orphan homeobox gene, Pem, that encodes a homeodomain (HD) that has undergone a surprisingly high rate of evolutionary change. The N-terminal portion of the Pem HD, which includes the first two alpha-helices, exhibits only 44% sequence identity between rat Pem (r.Pem) and mouse Pem (m.Pem). This N-terminal subdomain exhibited an extremely high frequency of nonsynonymous substitutions, severalfold higher than other regions of the Pem protein. In contrast, the third helix, which is known to confer most of the base-specific contacts of HDs with DNA, was almost identical in r. Pem and m.Pem. Several lines of evidence suggested that the rat and mouse genes that we identified as Pem genes are true homologues: (1) the r.Pem and m.Pem genes both reside on the X chromosome; (2) they possess identical exon/intron splice junctions; (3) they both encode a distinctive motif upstream of the HD that is unique to Pem; and (4) the only m.Pem-like gene we were able to identify in the rat genome other than r.Pem was a pseudogene, r.Pem-ps, whose sequence and chromosomal localization indicated that it was derived by reverse transcription and reinsertion into the genome. The functional r.Pem gene is selectively expressed in placenta, testis, epididymis, and ovary. This expression pattern is of interest since other genes transcribed in reproductive tissue have also been shown to undergo high rates of sequence divergence. The high rate of amino acid substitutions in the N-terminal region of the Pem HD suggests the possibility of species-specific directional selection.

Alternative Splicing↗
PubMed1996

Effect of petroleum ether extract from Hygrophila spinosa on hematological parameters and hepatorenal functions in mice.

Multiple doses of H. spinosa were administered, ip once in a week for 4 weeks (20, 40 and 80 mg/kg body weight) and daily for one month (2, 4 and 8 mg/kg body weight). No alteration in biochemical parameters at low and moderate dose level of daily and low dose level of weekly treatment of petroleum ether extract was observed. However, the extract at moderate dose level in weekly treatment changed serum aminotransferase, alkaline phosphatase and plasma cholesterol significantly. High dose level of the extract changed all the above parameters of weekly treated mice including total bilirubin, nonprotein nitrogen, blood urea and plasma protein. High dose level of daily treatment and moderate and high dose level of weekly treatment of the root extract increased only the white blood cell count significantly. The results reveal that the weekly moderate and high dose (above 40 mg/kg body weight) and daily/therapeutic high dose (8 mg/kg) of the petroleum ether extract of H. spinosa affects liver and kidney functions and metabolism and hematological parameters whereas low weekly dose (20 mg/kg) and low and moderate daily/therapeutic dose (2 and 4 mg/kg) does not exhibit any appreciable toxic action.

Alkanes↗
PubMed1995

Involvement of H1 and other chromatin proteins in the formation of DNA-protein cross-links induced by visible light in the presence of methylene blue.

The formation of DNA-protein cross-links (DPCs), induced by irradiation with visible light, was studied in methylene blue-treated (MB-treated) chromatin and H1-depleted chromatin. The effects of the MB concentration and radiation dose were studied using sodium dodecylsulphate-chloroform-isoamyl alcohol assay and sodium dodecylsulphate-polyacrylamide gel electrophoresis. Under identical experimental conditions, DPC formation was less in H1-depleted chromatin (70%) than in chromatin (92%). The non-histone proteins and core proteins of chromatin contributed towards DPC formation. Of the core proteins, H2A was more cross-linked than H4, whereas the bands for H2B and H3 melted into one in chromatin and H1-depleted chromatin. In both cases, the gel pattern showed the appearance of two new protein bands with approximate molecular weights of 27 kDa and 29 kDa as a result of histone-histone cross-linking. Viscometric studies showed that the dissociation of the compact structure of chromatin in 2 M NaCl was more extensive in irradiated, MB-treated, H1-depleted chromatin than in irradiated, MB-treated chromatin, indicating a reduction in the amount of DPC formation in H1-depleted chromatin.

Animals↗
PubMed1994

Femtosecond coherent transient infrared spectroscopy of reaction centers from Rhodobacter sphaeroides.

Protein and cofactor vibrational dynamics associated with photoexcitation and charge separation in the photosynthetic reaction center were investigated with femto-second (300-400 fs) time-resolved infrared (1560-1960 cm-1) spectroscopy. The experiments are in the coherent transient limit where the quantum uncertainty principle governs the evolution of the protein vibrational changes. No significant protein relaxation accompanies charge separation, although the electric field resulting from charge separation modifies the polypeptide carbonyl spectra. The potential energy surfaces of the "special pair" P and the photoexcited singlet state P* and environmental perturbations on them are similar as judged from coherence transfer measurements. The vibrational dephasing time of P* modes in this region is 600 fs. A subpicosecond transient at 1665 cm-1 was found to have the kinetics expected for a sequential electron transfer process. Kinetic signatures of all other transient intermediates, P, P*, and P+, participating in the primary steps of photosynthesis were identified in the difference infrared spectra.

Kinetics↗
PubMed1993

Picosecond infrared studies of the dynamics of the photosynthetic reaction center.

The changes in the vibrational transitions of the protein and redox cofactors of the photosynthetic reaction center were examined by picosecond infrared spectroscopy. The spectra in the vibrational mid-infrared region (1800-1550 cm-1) of hydrated and partially dehydrated reaction centers were investigated from 50 ps to 4 ns after photoinitiation of the electron transfer. Features in the infrared difference spectra were identified with both protein and redox cofactor vibrational modes and correlated with electron transfer events whose kinetics were measured in the infrared and visible regions. The observed protein response is confined to a few amide I transitions (1644 cm-1, 1661 cm-1, 1665 cm-1) and carboxylic residues (1727 cm-1). About 85% of the observed signal corresponded to alterations in the cofactor-associated ester and keto carbonyls. The amide I and carboxylic transitions appeared prior to 50 ps, suggesting that the primary electron transfer event is coupled with a specific piece of the protein backbone and to glutamic or aspartic residues nearby the special pair. Infrared absorption changes accompanying bacteriochlorophyll-dimer cation formation dominated the signal at all times investigated. Infrared spectral changes observed in hydrated and partially dehydrated reaction centers were distinctly different; a band at 1665 cm-1 with a spectral width of 6 cm-1 in the hydrated protein, corresponding to a protein amide I bleach, was not present in the dehydrated film. These differences are discussed in terms of the markedly different electron transfer kinetics observed in the presence of water.

Electron Transport↗
PubMed1992

Picosecond dynamics of bacteriorhodopsin, probed by time-resolved infrared spectroscopy.

The photoinduced reaction cycle of bacteriorhodopsin (BR) has been studied by means of a recently developed picosecond infrared spectroscopic method at ambient temperature. BR - K difference spectra between 1560 and 1700 cm-1 have been recorded at delay times from 100 ps to 14 ns. The spectrum remains unchanged during this period. The negative difference OD band at 1660 cm-1 indicates the peptide backbone responds within 50 ps. A survey in the region of carboxylic side chain absorption around 1740 cm-1 reveals that perturbations of those groups, present in low-temperature FTIR spectra, are not observable within 10 ns, suggesting a slow conformational change.

Bacteriorhodopsins↗
PubMed1991

Occurrence of pap-, sfa-, and afa-related sequences among F165-positive Escherichia coli from diseased animals.

A total of 160 Escherichia coli positive for F165 fimbrial antigen and isolated from diarrheic and septicemic animals, were examined for the presence of the pap, afa, and sfa/foc operons or related nucleotide sequences using colony hybridization. Most isolates shared DNA sequences with the pap operon sequences alone or in association with afa or sfa. Thus, our results indicate that F165-positive E. coli from diseased animals share DNA sequences with operons coding for adhesins important in human extra-intestinal disease and that multiple adhesin systems are often found in single isolates. However, 20% of the F165-positive isolates did not show any homology with the probes representing the three adhesin systems, suggesting that one of the operons responsible for F165 production could be different from the pap, sfa/foc, and afa operons.

Adhesins, Escherichia coli↗
PubMed1991

Bacteriophage lambda P gene shows host killing which is not dependent on lambda DNA replication.

Bacteriophage lambda, having a mutation replacing glycine by glutamic acid at the 48th codon of cro, kills the host under N- conditions; we call this the hk mutation. In lambda N-N-cl-hk phage-infected bacteria, the late gene R is expressed to a significant level, phage DNA synthesis occurs with better efficiency, and the Cro activity is around 20% less, all compared to those in lambda N-N-cl-hk(+)-infected bacteria. Segments of lambda DNA from the left of pR to the right of tR2, carrying cro, cII, O, P, and the genes of the nin5 region from the above hk and hk+ phages, were cloned in pBR322. Studies with these plasmids and their derivatives having one or more of the lambda genes deleted indicate that the hk mutation is lethal only when a functional P gene is also present. When expression of P from pR is elevated, due to the deletion of tR1, host killing also occurs without the hk mutation. We conclude that the higher levels of P protein, produced either (1) when cro has the hk mutation or (2) when tR1 is deleted, are lethal to the host. We also show that due to the hk mutation, the Cro protein becomes partially defective in its negative regulation at pR, resulting in the expression of P to a lethal level even in the absence of N protein-mediated antitermination. This P protein-induced host killing depends neither on lambda DNA replication nor on any other gene functions of the phage.

Amino Acid Sequence↗
PubMed1991

Isolation and preliminary characterization of Escherichia coli mutants resistant to lethal action of the bacteriophage lambda P gene.

Both spontaneous and NTG-induced mutants of Escherichia coli 594 insensitive to the lethal action of lambda P gene were isolated and called rpl (resistant to P lethality). These mutants were of two types, showing different phenotypes. On type I rpl mutants, lambda cl- and lambda v1v3 did not plate, while lambda vir, lambda cl- c17, lambda imm434, and lambda imm21 did; plasmid pMR45 carrying the lambda P gene could not complement lambda imm21P- phage in type I mutants. On the other hand, the type II rpl mutants support the growth of all the above phages including lambda cl-. Neither type of rpl mutation affects growth of the bacteria.

Bacteriophage lambda↗
PubMed1990

Visible light induced DNA-protein crosslinking in DNA-histone complex and sarcoma-180 chromatin in the presence of methylene blue.

Formation of DNA-protein cross-links by the action of visible light in the presence of methylene blue was studied in calf thymus DNA-calf thymus histone complex and sarcoma-180 chromatin. The extent of cross-link formation decreases with a decrease in the histone to DNA ratio in the DNA-histone complex. In chromatin, it is at a maximum (93%) at a dye to DNA nucleotide ratio (D/P ratio) of 0.04 and is appreciable even at a very low dye concentration (75% at a D/P ratio of 0.0033). Sepharose 4B-CL column chromatography indicates that methylene blue acts as a mediator in the cross-linking process, but not as a linker in the DNA-protein cross-link. Dodecylsulphate-polyacrylamide gel electrophoresis patterns reveal that both histone and non-histone proteins are involved in cross-linking, but to a varied extent. Competition experiments with ethidium bromide demonstrated the necessity of intercalative binding of methylene blue in the formation of DNA--protein cross-links. Viscometric studies in 2 M NaCl indicate that the compact structure of chromatin is stabilized by cross-linking.

Animals↗
PubMed1989

Further simplification of the general analysis of the intercalative drug-DNA interaction.

The application of McGhee and von Hippel's general equation [J. Mol. Biol., 86 (1974), 469-489, Eq. (15)] to the analysis of the interaction of intercalative drugs with DNA has been further simplified. The value of n can now be determined mathematically, using a simple function, and without any approximation. It is also established that the summation of squared deviation of (( (nu/c), nu)) points would be minimum for and only for the true set of (K,n,omega) of the interaction system. The method incorporating the simplification has been applied to determine the binding parameters of adriamycin-DNA interaction according to the above general equation.

Animals↗
PubMedDate not supplied

Androgen regulation of the Pem homeodomain gene in mice and rat Sertoli and epididymal cells.

Although the role of homeodomain transcription factors during embryogenesis is well known, their developmental function in postnatal animals is only beginning to be understood. We examined the regulation and expression pattern of Pem, a homeodomain protein that may regulate androgen-dependent events in the testis and epididymis. Immunohistochemical analysis showed that Pem protein is expressed selectively in the nuclei of Sertoli cells during the androgen-dependent stage of the seminiferous epithelium cycle in vivo. RNase protection analysis revealed that a proximal promoter was responsible for androgen-dependent mouse Pem expression in testis and epididymis in vivo, whereas a distal promoter was used in placenta. The mouse Pem gene was expressed at approximately 10-fold higher levels in the testis than in the epididymis; conversely, the rat Pem gene was expressed at >10-fold higher levels in the epididymis than in the testis. Because androgen-binding protein has been proposed to transport androgens from the testis to the epididymis, we tested whether the > or = 20-fold higher levels of androgen-binding protein expression in the rat, compared to that of mouse, are responsible for the differential expression of Pem in these two rodent species. Studies with androgen-binding protein transgenic mice demonstrated that the species-specific difference in androgen-binding protein expression is unlikely to be responsible for the species-specific difference in Pem expression. We found that androgen is necessary but not sufficient for Pem expression, since purified Sertoli cells rapidly down-regulated Pem transcripts in culture, regardless of the presence of testosterone. We conclude that Pem gene expression in Sertoli cells requires other cell types or cellular factors in addition to androgen.

Androgen-Binding Protein↗