Biomedical subjects

B R Krishnan

Publications and source records attributed to B R Krishnan.

22 records · Page 2Linked to original sources

PubMed1990

Mutations within the replicon of the IncN plasmid pCU1 that affect its Escherichia coli polA-independence but not its autonomous replication ability.

The minimal replicon of the incompatibility N group plasmid pCU1 is contained within a 2-kb DNA region of the plasmid. The ability of this region and of the deletion derivatives thereof, that are capable of autonomous maintenance, to direct polypeptide synthesis was examined. Two proteins of 27 and 5.5 kDa are encoded by the minimal replicon. Polypeptide chain-terminating mutations within the predicted open reading frame for the 27-kDa polypeptide abolished the synthesis of this polypeptide and also the Escherichia coli polA-independence phenotype of the pCU1 replicon. However, these mutations did not affect the autonomous replication ability of the pCU1 replicon in wild-type E. coli and the expression of incompatibility towards the parental plasmid.

Amino Acid Sequence↗

PubMed1990

IncN plasmid replicon. A deletion and subcloning analysis.

A DNA segment of approximately 2000 base-pairs bounded by restriction enzyme sites for PvuII and containing the minimal replicon of an N group plasmid was characterized. A natural derivative of this miniplasmid was found to have undergone a deletion within one of two tandem iteron families, the group I iterons. Further analysis showed that all plasmid-determined functions essential for stable maintenance in Escherichia coli were localized to a contiguous region of DNA of 1019 nucleotides that excludes entirely these iterons. However, the loss of these iterons led to an increase in plasmid copy number. This indicates that members of the group I iteron-family have a role in determining plasmid copy number perhaps by titrating a plasmid-specified trans-acting product. The 2000 base-pair segment contains six open reading frames of 40 or more amino acid residues. The essential segment contains a 368 nucleotide region that must be present in cis and within which there are three "GATC" sequences and a putative Escherichia coli DnaA protein-binding sequence (dnaA box). An interesting feature is that the cis-acting region is present entirely within a presumptive rep gene. The essential segment contains four open reading frames, only one of which has an Escherichia coli canonical ribosome-binding site. The 2000 base-pair miniplasmid has two separable regions determining N group plasmid incompatibility.

Bacterial Proteins↗

PubMed1988

Host Ranges of the IncN Group Plasmid pCU1 and Its Minireplicon in Gram-Negative Purple Bacteria.

The bacterial host ranges of the conjugatively self-transmissible IncN group plasmid pCU1 and its mobilizable miniderivative, pCU785, were examined. Species of the gram-negative purple bacteria were chosen for this study. Conjugative mobilization of pCU785 into a wide variety of bacteria was facilitated by the presence of oriT of the broad-host-range plasmid RK2 in pCU785. Although the host range of the IncN tra system of pCU1 is broad, the host range of its replicon is limited. However, the pCU1 replicon can be maintained in Agrobacterium, Bradyrhizobium, and Rhizobium species under conditions that select for plasmid maintenance. It is lost efficiently from these populations on release of selection.

Journal Article↗

PubMedDate not supplied

Genetic analysis of a group of mentally retarded children.

Genetic analysis of 169 mentally retarded (MR) children from Madras, revealed chromosomal abnormalities in 17%. Down syndrome was the major chromosomal anomaly (24/169 = 14.2%). These included three cases of trisomy-21 mosaics, and one case of de novo Robertsonian translocation. MR children with chromosomal abnormalities were either mildly or moderately retarded. Syndromes with known etiology occurred in 3% of the MR cases. Microcephaly, neonatal anoxia, perinatal stress and pharmacological attempt for abortion were found to be important pathogenic factors associated with MR. Most of the microcephalics (11/169 = 6.5%) were severely retarded, whereas those associated with neonatal anoxia and perinatal stress were either mildly or moderately retarded. Birth-order effects were found only among Down syndrome patients. Segregation analysis of the three groups of proband families (viz. mild, moderate and severe MR) indicated that autosomal recessive mode of inheritance is compatible in moderate and severe MR proband families. The proportion of X-linked instances of MR is estimated to be about 22% of the cases.

Child↗