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R Zoorob

Publications and source records attributed to R Zoorob.

33 records · Page 2Linked to original sources
PubMed1994

Two Mhc class I and two Mhc class II genes map to the chicken Rfp-Y system outside the B complex.

Gene sequences highly similar to major histocompatibility complex (Mhc) class I and class II genes were recently recognized as mapping to a site in the genome of the chicken separate from the Mhc class I, class II, and B-G genes of the major histocompatibility (B) complex. The present study was undertaken to see whether this complex of Mhc-like genes designated as restriction fragment pattern Y (Rfp-Y) might reside in one of three clusters of cosmid clones contained within the molecular map of chicken Mhc genes, since only two of the three clusters can be assigned to the B system. To determine whether the third cluster (cluster II/IV) might contain Rfp-Y, a subclone (18.1) from within cluster II/IV near a polymorphic lectin gene was used to analyze the DNA of families in which Rfp-Y haplotypes are known to be segregating. The restriction fragment polymorphisms revealed by the 18.1 probe were found to segregate in parallel with the restriction fragment polymorphisms defining the Rfp-Y haplotypes, thus establishing the location of Rfp-Y within cosmid cluster II/IV. Two of six Mhc class I genes and two of five Mhc class II genes map to cosmid cluster II/IV, so a substantial fraction of chicken Mhc genes, including at least one that may be expressed, are located in a chromosomal region separate from the B system. In further linkage analyses, Rfp-Y was found to assort independently from more than 400 markers in the present linkage map of the chicken genome.

Alleles↗
PubMed1994

Molecular characterization of three Mhc class II B haplotypes in the ring-necked pheasant.

We investigated the class II B genes in a free-ranging population of the ring-necked pheasant Phasianus colchicus by a combination of restriction fragment length polymorphism (RFLP), polymerase chain reaction (PCR), and DNA sequencing. Special attention was paid to the variation in the second exon, which encodes the peptide-binding beta 1-domain. The population was introduced, but it still exhibited major histocompatibility complex polymorphism with at least three segregating class II B haplotypes and consequently six genotypes. We found two class II B genes associated with each haplotype. The class II B genes of birds had until then only been molecularly characterized in the domestic chicken. The pheasant genes were highly variable, although one of the amplified sequences was found in two different haplotypes. Taken together, the most polymorphic positions (residues 37 and 38) were not identical in any of the predicted protein sequences, but all except one of the motifs had already been found in the domestic chicken. Structurally important features in mammalian class II B genes were generally conserved also in the pheasant sequences, but the loss of a potential salt bridge constituent (Arg72) in several sequences may suggest a slightly different structure of the adjacent parts of the peptide-binding groove. The pheasant genes are most closely related to the so called B-LBII family in the chicken, indicating that this represents a major line of development among avian class II B genes.

Amino Acid Sequence↗
PubMed1994

Linkage of a new member of the lectin supergene family to chicken Mhc genes.

With the use of tissue-specific cDNA probes, several genes, which do not correspond to the class I (B-F), class II (B-L), or class IV (B-G) genes, were detected within the cosmid clusters containing the chicken major histocompatibility genes. We isolated cDNA clones with a probe corresponding to one of them, the 17.5 gene, located between two class I genes. The 17.5.3 cDNA, isolated from a chicken spleen cDNA library, encodes a 257-residue-long protein. This sequence shows significant similarity with several members of the C-type animal lectin superfamily and is probably a type II transmembrane protein. Analysis of several cDNA clones, together with Southern blot experiments, strongly suggest that this gene belongs to a multigene family, with at least some of its members being polymorphic. Several arguments lend support to the possibility that, together with the linked Mhc genes, the 17.5 gene is part of the recently described Rfp-Y system.

Amino Acid Sequence↗
PubMed1993

Chicken major histocompatibility complex class II B genes: analysis of interallelic and interlocus sequence variance.

Five different chicken B-LB genes were cloned and sequenced. The comparison of these sequences shows that they can be classified as members of two different families, the B-LBII family (containing the B-LBI and B-LBII genes) and the B-LBIII family (containing the B-LBIII, B-LBIV, and B-LBV genes). The extent of polymorphism within each of these families was assessed by in vitro amplification of DNA fragments encompassing exon 2 in several haplotypes. The nucleotide sequences were determined, and pairwise relationships were evaluated. In the course of this work, a sixth gene termed B-LBVI was identified, defining a third family (B-LBVI family). Polymorphism of the B-LBIII or B-LBVI families is far less extensive than that of the B-LBII family. In this latter, the distribution of conserved and polymorphic residues is similar to what has been described in mammals. These families seem to have been generated by gene duplication events giving rise to several isotypes, as observed in mammals. However, phylogenetic analyses indicate that these families are not homologous to their mammalian counterparts. Evaluation of the level of transcription of these different genes showed that genes from the B-LBII family are predominantly transcribed over those of the other families.

Alleles↗
PubMed1990

Organization of a functional chicken class II B gene.

Five class II (B-L) B genes are encoded in the major histocompatibility complex (MHC) of chickens of the B12 haplotype. We report here the nucleotide sequence of one of these genes, B-LBII, as well as the primary structure of a corresponding cDNA. The organization of B-LBII, its 5' flanking region including the promotor region, and the amino acid sequence of its product are compared to mammalian class II B genes and to the previously described B-LBIII gene, which probably is a pseudogene since no B-LBIII transcript could be identified. The 5' flanking region of B-LBII exhibits homologs of transcription-controlling sequence motifs, namely S, X, X2, and Y boxes, of class II A and B genes of rodents and man. However, the promotor region of B-LBIII lacks an equivalent of the S box, displays two nucleic acid substitutions in the core sequence of the Y box, and exhibits a 16 base pair (bp) deletion upstream of the site of initiation of transcription. Therefore, an aberrant promotor region is likely to account for the pseudogene-like nature of B-LBIII, which displays open-reading frames in all exons. The data obtained with the functional B-LBII gene are in line with our previous interpretation that both genomic organization and tertiary structure of class II beta molecules are remarkably conserved between birds and mammals.

Amino Acid Sequence↗
PubMed1988

Isolation of chicken major histocompatibility complex class II (B-L) beta chain sequences: comparison with mammalian beta chains and expression in lymphoid organs.

By cross-hybridization in low stringency conditions, using a probe derived from an HLA-DQ beta cDNA clone, we have isolated several chicken genomic DNA clones. These clones were mapped to the major histocompatibility complex (MHC) of the chick (B complex) by virtue of their ability to detect restriction enzyme length polymorphisms between congenic lines of chicken. Evidence was obtained for the presence of at least three B-L beta genes in the chicken genome. The B-L beta genes are transcribed specifically in tissues containing cells of the B lymphocyte and myeloid lineages and expressing the B-L antigens. Exons encoding the beta 1, beta 2 and transmembrane domains of a B-L beta chain have been identified with 63, 66 and 62% similarity with the HLA-DQ beta sequence. This first isolation of an MHC class II gene outside of the mammalian class provides insight into the evolution of MHC genes based on the comparison of avian and mammalian class II beta chain amino acid and nucleotide sequences.

Amino Acid Sequence↗
PubMed1988

A molecular map of the chicken major histocompatibility complex: the class II beta genes are closely linked to the class I genes and the nucleolar organizer.

We have cloned in a cosmid vector four DNA clusters covering 320 kb of the chicken MHC (B complex), including five class II (B-L) beta genes defining two related isotypic families. Additional B complex genes have been revealed using tissue-specific cDNA probes. A cosmid fragment has been used to isolate a cDNA for a class I (B-F) transcript. This transcript, that is by far the most divergent known member of the class I gene family, hybridized to six B-F genes present in the cosmids. One of the clusters was shown to contain two rRNA transcriptional units from the nucleolar organizer region (NOR), marking the telomeric boundary of the B complex. None of the other B complex genes hybridizes to, or has the transcriptional characteristics of mammalian MHC class II alpha or class III genes. The map we have obtained shows that the B complex does not contain well defined class I and class II regions since B-F and B-L beta genes are closely associated with unrelated genes. Moreover, class II beta genes are very closely linked to class I genes in two clusters, and to the NOR in a third one.

Amino Acid Sequence↗
PubMed1988

Molecular analysis of chicken immune response genes.

We have recently isolated immune response genes of the major histocompatibility B complex of the chicken (the B-L beta genes) by cross-hybridization in low stringency with an HLA class II beta chain probe. After reviewing the main results obtained, we present a detailed analysis of the region flanking the first gene characterized, B-L beta III. By Southern blot analysis with exon-specific probes, we demonstrate the presence of another related B-L beta gene 10 kb on the 3' side of B-L beta III, the B-L beta V gene. Moreover, retrospective analysis of the phage clones initially isolated with the HLA-DQ beta probe, using a chicken class I probe that we isolated by chromosome walking from the B-L beta genes, indicates that the B-L beta III gene is closely linked on its 5' side to a class I gene, B-FVI.

Amino Acid Sequence↗
PubMedDate not supplied

Family medicine in Lebanon: the 10th anniversary.

Developing a family practice residency program was a logical step in addressing the needs for primary care in Lebanon. The American University of Beirut initiated a family practice residency program in 1979. The curriculum was structured following the guidelines of the American Academy of Family Physicians. Since its establishment, the program has participated in the design, launching, and maintenance of the family practice residency in Bahrain. Future plans include establishing other programs in the region and increasing community participation.

Delivery of Health Care↗