Biomedical subjects

A C Christensen

Publications and source records attributed to A C Christensen.

22 records · Page 2Linked to original sources

PubMed1982

T4 late transcripts are initiated near a conserved DNA sequence.

Bacteriophage T4 late transcription is unusual, among prokaryotes, in its complexity. Late transcription requires the host RNA polymerase, the products of T4 genes, 33, 45 and 55, and other small polypeptides, the genes of which have not been identified. In addition the DNA template must be "competent' for late transcription. First the DNA must contain the substituted base 5-hydroxymethyl cytosine in place of cytosine (this requirement is eliminated by a mutation in the T4 alc gene). Second, the DNA must be replicating, although late transcription can be uncoupled from DNA replication by mutations in the T4 genes coding for DNA ligase (gene 30) and DNA exonuclease (gene 46). We report here the location of the initiation sites of the messenger RNAs (mRNAs) synthesized in vivo from four late genes (genes 21, 22, 23 and 36) by S1 nuclease mapping and we have determined the DNA sequences at these sites. We have found strong homology to the sequence TATAAATACTATT immediately upstream from the 5' ends of the late messages and we suggest that this sequence is specifically recognized by the complex responsible for late transcription. Also, we have examine gene 23 mRNA synthetized in the absence of DNA replication using the 30- 46- mutant described above and find that it is identical to the true late transcript synthesized in normal infections.

Base Sequence↗

PubMed1980

Factors affecting efficacy of methionine hydroxy analogue for chicks fed amino acid diets.

Chicks were fed mixtures of methionine, cystine, and the calcium salt of the hydroxy analogue of methionine (MHA) in a diet based on a mixture of amino acids. Rate of gain with the basic amino acid diet containing a mixture of methionine and cystine was about 90% of the rate noted with a practical type diet. Efficacy of MHA depended on its level in the diet and on the levels of methionine and cystine fed with it. It was least effective when fed as the only sulfur amino acid or when fed with cystine. When fed with methionine it had intermediate value and was most efficacious when fed with a mixture of methionine and cystine. Essentially it was fully effective when it provided 25% of the sulfur amino acids with the remainder as equal parts of methionine and cystine. Replacing part of the cystine in a mixture of cystine and MHA with methionine resulted in a marked improvement in performance with L-methionine being slightly more effective than D-methionine.

Amino Acids↗

PubMed1980

Factors affecting efficacy of methionine hydroxy analogue for chicks fed practical diets.

The relative values of the calcium salt of the hydroxy analogue of methionine (MHA) and L-methionine were studied in chick feeding tests with five practical type diets deficient in the sulfur amino acids. Performance was improved with the addition of either substance to each of the five diets. Methionine was slightly more effective at low levels of addition to the four diets primarily deficient in methionine. The two supplements were equally effective in one diet based on corn, soybean, and meat and bone meals, a diet with a wider methionine/cystine ratio. Both the practical and highly purified amino acid diets thus showed similar differences in efficacy of the two products as the methionine/cystine ratio of the diet changed. Methionine also was more effective than MHA in overcoming the deleterious effects produced by the addition of ethionine to a practical type diet.

Animals↗

PubMed1978

Effect of transferrin saturation on iron delivery in rats.

Studies were carried out in rats to evaluate the release of iron from monoferric and diferric transferrin. Isoelectric focusing was carried out on plasma tagged at low and high saturations, and it was shown that these represented primarily monoferric and diferric transferrin, respectively. In vivo studies with these tagged plasmas were carried out on normal, iron-deficient, and hypertransfused rats. In all three groups there was a greater in vivo uptake of iron from diferric transferrin by all tissues monitored. Though the amount varied in different animals, the ratio of uptake between diferric and monoferric transferrin iron varied between 1.56 and 2.10 in the erythron and between 2.38 and 2.65 in the liver. These studies indicate that changes in transferrin saturation, by changing the proportion of monoferric to diferric transferrin iron, changed the amount of iron released to tissues.

Animals↗