Periodicity in DNA coding sequences: implications in gene evolution

In this paper we have employed Fourier analysis of DNA coding and non-coding sequences in an attempt to identify possible patterns in gene sequences. It was found that while intronic sequences show a rather random pattern, coding sequences show periodicities and in particular a periodicity of 3. We were able to reconstruct such patterns by assuming a gene having one codon occurring in about 40% of the sequence. This could indicate that the predominant presence of codons all starting from the same base could confer the observed periodicities. Indeed, it was found that proteins do obey this rule. Implications of this finding in gene evolution are discussed.     

Flow cytometry reveals different lag times in rapid cytoplasmic calcium elevations in human neutrophils in response to N-formyl peptide

Flow cytometric analyses were performed to study intracellular single-cell calcium transients ([Ca²⁺]_i) in suspended human neutrophils during the initial phase of N-formyl peptide stimulation. Thereby, two neutrophil populations became apparent. Early maximally Ca²⁺-responding (high fluorescence) neutrophils and not-yet Ca²⁺-responding (low fluorescence) neutrophils, but no neutrophils with intermediate levels of [Ca²⁺]_i, were detected. Within 7 s the number of low fluorescence neutrophils decreased and the number of high fluorescence neutrophils increased maximally. This suggests that [Ca²⁺]_i transients occurred abruptly in individual neutrophils within a time interval below 1 s. At lower N-formyl peptide concentrations the lag times of individual neutrophils and the interval time of maximal activation of the [Ca²⁺]_i-responding neutrophil population increased, however the percentage of [Ca²⁺]_i-responding cells decreased. Surprisingly, no influence of the N-formyl peptide concentration on the [Ca²⁺]_i-induced fluorescence signal of the individual cell was observed: it was always in an almost maximal range or not responding. In parallel, binding studies performed with fluorescein-labeled N-formyl peptide revealed that the heterogeneity of [Ca²⁺]_i-responding cells cannot be explained by different receptor occupancy. In summary, this study demonstrates that [Ca²⁺]_i transients induced by N-formyl peptides in suspended individual human neutrophils occur very rapidly in an almost “all-or-none manner” and that the mean increasing fluorescence signal of a calcium indicator within a whole neutrophil population results from varying lag times of the individual cells, rather than from the mean simultaneous progress of many cells. © 1993 Wiley-Liss, Inc.     

VASOMOTOR RESPONSES OF ISOLATED PERIPHERAL BLOOD VESSELS FROM BOWHEAD WHALES: THERMOREGULATORY IMPLICATIONS

Temperature regulation in bowhead whales, Balaena mysticetus , is supported by the characteristic cetacean peripheral circulation, especially notable in the tail flukes. Blood vessels serving this function consist of countercurrent heat exchangers (network of veins surrounding a central artery) favoring heat conservation and an alternate routing via arteriovenous anastomoses (AVAs) providing for heat dissipation. We tested the vasomotor responses of isolated segments of countercurrent arteries and AVAs from the bowhead tail flukes to norepinephrine (NOR), the sympathetic adrenergic neurotransmitter. Isometric tension developed during exposure to a micromolar concentration of NOR was consistently higher in AVAs than in arteries. Accordingly, the AVAs are subject to sympathetic vasoconstriction, and this activation directs blood flow to countercurrent heat exchangers and results in heat conservation. In contrast, AVA relaxation by reduced sympathetic activation favors increased blood flow through AVAs and consequent peripheral heat loss.     

Resolution of 4-chlorobenzoate dehalogenase from Pseudomonas sp. strain CBS3 into three components.

Extracts of Pseudomonas sp. strain CBS3 grown with 4-chlorobenzoate as sole carbon source contained an enzyme that converted 4-chlorobenzoate to 4-hydroxybenzoate. This enzyme was shown to consist of three components, all necessary for the reaction. Component I, which had a molecular weight of about 3,000, was highly unstable. Components II and III were stable proteins with molecular weights of about 86,000 and 92,000.