Comparison of two platelet count estimation methodologies for peripheral blood smears.

Objective: To compare two manual methods for estimating platelet counts from Wright's stained peripheral blood smears regarding their correlation with each other and with automated platelet counts. This correlation was examined in relation to whether the platelet count was high, low, or normal and in relation to whether the hemoglobin value was low versus normal or high.

Design: Peripheral blood smears were Wright's stained and both platelet count estimation methodologies were performed on each slide.

Increased isoleucine acceptance by sulfur-deficient transfer RNA from Escherichia coli.

Sulfur-deficient tRNA, isolated from Escherichia coli HfrC, rel-, met-, cys-, lambda, after cysteine starvation, was found to have an increased acceptance of isoleucine in proportion to the deficiency of 4-thiouridine. Isoleucine acceptance was not altered in the presence of other amino acids of CTP, and the higher acceptance was observed over a wide range of magnesium, isoleucine, tRNA and enzyme concentrations. The Vmax value for sulfur-deficient tRNA was more than three times greater than observed for normal tRNA.

Sulfur-deficient transfer ribonucleic acid in a cysteine-requiring, "relaxed" mutant of Escherichia coli.

A cysteine-requiring mutant of the parent strain Escherichia coli Hfr Cavalli (RC(rel), Met(-), lambda) has been isolated. The mutant was selected by using replica plating after mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine. The mutation appears to be in the gene for sulfite reductase, since the mutant could utilize sulfide but not sulfite as a sulfur source.