Search PubMed⌕ Search

Biomedical subjects

L K Johnson

Publications and source records attributed to L K Johnson.

106 records · Page 6Linked to original sources
PubMed1978

Developmental transitions between chromatin-bound and soluble RNA polymerase subspecies in the soybean hypocotyl.

RNA polymerase enzymes isolated from soybean hypocotyl tissue during successive developmental stages (2-8 days old) have been fractionated by Sephadex column isoelectric focusing. Both the enzymes bound to chromatin and those enzymes free in the soluble phase were investigated during development with respect to their distribution within these two pools. All observed activites were classified according to their alpha-amanitin sensitivity and isoelectric points. Two Class I subspecies (Ia, Ib) and two Class III subspecies (IIIa, IIIb) were continually present bound to chromatin throughout the developmental sequences except the IIb form which was absent at the latest stage. However, a great multiplicity (9 total) of Class II activities (totally inhibited by alpha-amanitin) were observed to be bound to chromatin at the 2nd day stage. These forms were first released from the chromatin complex and recovered in a soluble pool (4th day stage). Subsequent hypocotyl development was accompanied by the gradual disappearance of these Class II subspecies from this pool (6th day) until only two soluble species and one chromatin-bound Class II activity remained (8th day). These observations indicate that the early development of this tissue is accompanied by a dramatic alteration in the conplexity of chromatin-bound RNA polymerase subspecies. Such events may in part determine the domain of RNA secies synthesized at successive developmental stages.

Chromatin↗
PubMed1978

Developmental restrictions on hormone modulated gene transcription. II. Hormone induced interactions of RNA polymerase with chromatin.

Chromatin-bound and soluble RNA polymerase subspecies have been isolated and fractionated by isoelectric focusing at various times (0, 6, 12 and 18 h) following auxin treatment of 4 day (responsive) and 8 day (unresponsive) soybean hypocotyls. Young 4 day seedlings displayed two well defined phases of auxin induced gene transcription. Phase I (6 h) evidenced the selective dissociation of many RNA polymerase subspecies from the chromatin complex which was accompanied by the retention of three class II enzymes. Phase II occurred after 12 h of treatment when the dissociated enzymes including some species which were soluble in the 0 h controls became re-associated with chromatin. These induced RNA polymerases may be responsible for the synthesis of auxin induced RNAs. In contrast, the unresponsive 8 day hypocotyl did not display two phases of auxin induction. Phase one, the dissociation of the chromatin bound enzymes, occurred at 12 h (compared to 6 h for the 4 day seedling) and was not followed by the later translocation of any soluble enzymes towards the chromatin complex. The results support earlier findings suggesting that the developmental "phasing out" of RNA polymerase subspecies limits the hormone induced growth response of this tissue and thus is regarded as an off switch for the transcription of such hormone controlled gene sequences.

2,4-Dichlorophenoxyacetic Acid↗
PubMedDate not supplied

Purification, sequencing and synthesis of natriuretic and vasoactive rat atrial peptide.

Mammalian atria contain potent natriuretic and diuretic substances which exist in high- and low-molecular-weight forms and which appear to be associated with atrium-specific granules. The natriuretic effect of atrial extract is largely accountable for by its renal haemodynamic effects; atrial extracts also antagonize hormone- and non-hormone-induced contraction of the isolated rabbit aorta and isolated rat kidney vasculature. We have completely purified a low-molecular-weight natriuretic and vasoactive substance from rat atria and characterized it as a 24-amino acid peptide. Synthetic peptide, produced by solid-phase synthesis, mimics biological effects of crude atrial extract and purified peptide; its activity is enhanced by slow oxidation, suggesting a disulphide (Cys 4-Cys 20) configuration for the native peptide. If secreted into blood, this atrial natriuretic peptide (' auriculin B') could be a novel peptide hormone of considerable importance to renal and cardiovascular homeostasis.

Amino Acid Sequence↗
PubMedDate not supplied

Dose-titration to confirm the level of fenbendazole for control of Raillietina cesticillus in broiler chickens.

A total of 452 broiler chickens, naturally infected with Raillietina cesticillus, were allotted into six treatment groups. One group was fed unmedicated broiler ration (Group 1), and the other five groups were fed broiler ration containing fenbendazole at 180 ppm for 3 days (38.5 mg/kg body weight [BW]), 240 ppm for 3 days (50.9 mg/kg BW), 120 ppm for 6 days (52.2 mg/kg BW), 180 ppm for 6 days (79.9 mg/kg BW), or 240 ppm for 6 days (104.3 mg/kg BW). Fenbendazole was 100.0% efficacious against R. cesticillus when administered in the diet at 240 ppm for 6 days; 99.9% at 240 ppm for 3 days and at 180 ppm for 6 days; 99.5% at 120 ppm for 6 days; and 96.9% at 180 ppm for 3 days. Fenbendazole treatment had no adverse effect on weight gain or feed intake.

Animals↗