Selection for bacteriophage latent period length by bacterial density: A theoretical examination

In bacteriophage (phage), rapid and efficient intracellular progeny production is of obvious benefit. A short latent period is not. All else being equal, a longer latent period utilizes host cell resources more completely. Using established parameters of phage growth, a simulation of three successive phage lysis cycles is presented. I have found that high, but not low, host cell densities can select for short phage latent periods. This results from phage with short latent periods more rapidly establishing multiple parallel infections at high host cell concentrations, whereas phage with long latent periods are restricted to growth within a single cell over the same period. This implies that phage with short latent periods habitually grow in environments that are rich in host cells.     

Action of aldosterone on cultured renal collecting duct cells during the latent period.

The effects of aldosterone on protein synthesis in the latent period were investigated on cultured renal collecting duct cells from neonatal rabbit kidneys. Tissue was incubated with radioactively labelled uridine and amino acids and then precipitated with trichloroacetic acid in order to determine the intracellular precursor pool and identify new synthesis of RNA and protein. During the latent period, aldosterone increased the intracellular radioactive uridine pool and total radioactive RNA content already 20 and 60 min after its application; conversely 40 min after aldosterone introduction, no stimulation was found. Further experiments revealed that the intracellular radioactive amino acid pool was generally increased by aldosterone after 20, 40 and 60 min, while a distinct increased radioactive protein content was found to be induced by aldosterone only after 40 min. This indicates that aldosterone increases the uptake of RNA and protein precursors and the new synthesis of RNA and proteins. These events seem to to be regulated not continuously but intermittently. The induced proteins possibly take part in the mediation of the early hormone response. Experiments with the aldosterone antagonist, spironolactone, provide evidence for the specificity of the described hormone effects. The results after application of the Na+ channel blocker, amiloride, and the Na+/K(+)-ATPase inhibitor, G-strophanthin, indicate that the aldosterone effects are controlled by Na+ channels and Na+ pumps and therefore by the intracellular Na+ content. The inhibitory effect of cycloheximide on the aldosterone-induced protein synthesis indicates the role of these proteins on the hormone-stimulated Na+ transport.     

Action spectrum of Drosophila cryptochrome

Cryptochromes are a highly conserved class of UV-A/blue light photoreceptors. In Drosophila, cryptochrome is required for the normal entrainment of circadian rhythms to light dark cycles. The photocycle and molecular mechanism of animal cryptochrome photoreception are presently unknown. Drosophila cryptochrome undergoes light-dependent degradation when heterologously expressed in Schneider-2 cells. We have generated Drosophila luciferase-cryptochrome fusion proteins to more precisely monitor light-dependent cryptochrome degradation. We found that the luciferase-cryptochrome fusion protein undergoes light-dependent degradation with luciferase activity declining approximately 50% within 5 min of light exposure and approximately 85% within 1 h of light exposure. Degradation is inhibited by MG-132, consistent with a proteasomal degradation mechanism. Irradiance-response curves yield an action spectrum similar to absorption spectra for prokaryotic and eukaryotic cryptochromes with highest sensitivity in the UV-A. A luciferase-cryptochrome fusion protein lacking the terminal 15 amino acids is stably expressed in the dark but demonstrates increased sensitivity to light-induced degradation. The conferral of light-dependent degradation on a heterologous protein by fusion to cryptochrome may be a useful tool for probing protein function in cell expression systems.     

Dose-dependent latent period and periodicity of infectious diseases

This paper presents a theoretical analysis of an SEIRS epidemiological model. It shows that nonlinearity due to a dose-dependent latent period can cause periodicity through a Hopf bifurcation.     

Action spectrum of Kluyveromyces lactis mycocins

New mycocinogenic strains of the yeast Kluyveromyces lactis were found. They have fungicidic activity at pH from 5 to 7. This activity was eliminated by UV irradiation. Among over 260 species tested, ones sensitive to these mycocins were revealed mainly in the families Saccharomycetaceae and Wickerhamomycetaceae of the order Saccharomycetales.