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Biomedical subjects

H Chan

Publications and source records attributed to H Chan.

At least 163 records · Page 9Linked to original sources
PubMed1977

RNA polymerase binding sites in lambdaplac5 DNA.

The in vitro binding of the Escherichia coli RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) to fragments of lambdaplac5 DNA generated by restriction endonucleases HindII and HindIII has been studied by a filter binding technique. The results are consistent with RNA polymerase binding at p(R)', the INT promoter (p(I)), several sites in the b2 region, the mis promoter, the oop promoter (or p(O)), and p(rm). Binding was also observed on some fragments that are not known to contain active promoters, including the fragment from the cIII-t(L) region. Some of these binding reactions might also be explained by interaction of RNA polymerase with termination sites. Additional polymerase binding sites have been detected by examining which HindII and HindIII sites were not cleaved when digestion was performed after RNA polymerase had been bound to the DNA. This technique revealed polymerase binding at p(L), at p(R), at a site between R and cos, and at a site at the junction of the gamma and cIII-t(L) fragments. A comparison of the location of polymerase binding fragments with the partial denaturation map of the lambda genome indicates that RNA polymerase binding sites are located within A-T rich regions. It is suggested that RNA polymerase binding is a function both of specific sequences (where recognition occurs) and of the base composition of the surrounding regions (which affects the stability of the helix at the specific site).

Binding Sites↗
PubMed1977

A new familial cancer syndrome? A spectrum of malignant and benign tumors including retinoblastoma, carcinoma of the bladder and other genitourinary tumors, thyroid adenoma, and a probable case of multifocal osteosarcoma.

An 11-year-old Caucasian girl who had been cured of bilateral retinoblastoma developed non-radiation-induced osteosarcoma in multiple sites of the extremities. Investigation of the medical histories of 36 of her family members through six generations revealed that 8 relatives on the maternal side (22%) had malignant tumors, predominately genitourinary carcinomas, 2(6%) had benign tumors only, and 2(6%) had both benign and malignant neoplasms. The histologic variety of these tumors, the predominance of genitourinary carcinoma, the higher than expected frequency of tumor appearance over six generations, and the occurrence of malignant tumors in direct lineage suggest that the case of retinoblastoma followed by osteosarcoma is part of a familial cancer syndrome.

Adenoma↗
PubMed1977

Lead poisoning from ingestion of Chinese herbal medicine.

A 4-month-old infant was proven to have acute plumbism attributed to the ingestion of lead-containing Chinese herbal medicines. The analyses of 11 brands of Chinese herbal medicines by flameless atomic absorption spectrophotometry revealed that one of the medicines, Po Ying Tan, made by company A, had a mean lead content of 7.5 mg per unit dose; the other 10 brands had lower but still significant lead contents. In Chinese communities, these medicines are used very frequently, without prescription, for many minor ailments. This practice places a large number of individuals at risk for acute and chronic lead poisoning.

Edetic Acid↗
PubMed1969

Discrete conductance fluctuations in lipid bilayer protein membranes.

Discrete fluctuations in conductance of lipid bilayer membranes may be observed during the initial stages of membrane interaction with EIM ("excitability inducing material"), during destruction of the EIM conductance by proteolysis, and during the potential-dependent transitions between low and high conductance states in the "excitable" membranes. The discrete conductance steps observed during the initial reaction of EIM with the lipid membranes are remarkably uniform, even in membranes of widely varying lipid composition. They range only from 2 to 6 x 10(-10) ohm(-1) and average 4 x 10(-10) ohm(-1). Steps found during destruction of the EIM conductance by proteolysis are somewhat smaller. The transition between high conductance and low conductance states may involve steps as small as 0.5 x 10(-10) ohm(-1). These phenomena are consistent with the formation of a stable protein bridge across the lipid membrane to provide a polar channel for the transport of cations. T6he uniform conductance fluctuations observed during the formation of these macromolecular channels may indicate that the ions in a conductive channel, in its open state, are largely protected from the influence of the polar groups of the membrane lipids. Potential-dependent changes in conductance may be due to configurational or positional changes in the protein channel. Differences in lipid-lipid and lipid-macromolecule interactions may account for the variations in switching kinetics in various membrane systems.

Electric Conductivity↗
PubMed1969

Chromosome replication in Salmonella typhimurium.

The replication of the Salmonella typhimurium chromosome was studied. As with E. coli 15T(-), replication was sequential. After amino acid starvation, replication proceeded from a unique and heritable region of the chromosome. 5-Bromouracil, when substituted for thymine, did not disturb the sequence of replication nor did it initiate extra replication cycles. By labeling the origin and the terminus of the chromosome with (3)H- and (14)C-thymine, respectively, it was possible to determine that the rate of chain elongation decreases as the growth rate decreases. No gap in the replication cycle could be observed.

Amino Acids↗