Histone methyltransferase SUV39H1 participates in host defense by methylating mycobacterial histone‐like protein HupB

Host cell defense against an invading pathogen depends upon various multifactorial mechanisms, several of which remain undiscovered. Here, we report a novel defense mechanism against mycobacterial infection that utilizes the histone methyltransferase, SUV39H1. Normally, a part of the host chromatin, SUV39H1, was also found to be associated with the mycobacterial bacilli during infection. Its binding to bacilli was accompanied by trimethylation of the mycobacterial histone‐like protein, HupB, which in turn reduced the cell adhesion capability of the bacilli. Importantly, SUV39H1‐mediated methylation of HupB reduced the mycobacterial survival inside the host cell. This was also true in mice infection experiments. In addition, the ability of mycobacteria to form biofilms, a survival strategy of the bacteria dependent upon cell–cell adhesion, was dramatically reduced in the presence of SUV39H1. Thus, this novel defense mechanism against mycobacteria represents a surrogate function of the epigenetic modulator, SUV39H1, and operates by interfering with their cell–cell adhesion ability.     

Methods of cell lysis and effect of detergents for the recovery of nitrile metabolizing enzyme from Amycolatopsis sp. IITR215

Nitrile metabolizing enzymes are of great industrial interest for the selective bio-transformation of nitriles and surface modification of synthetic polymers under mild reaction conditions. In the present work, isolated strain Amycolatopsis sp. IITR215 was cultivated in the bench top bioreactor for the recovery of maximum biomass of whole cell catalyst. Effect of different lyoprotectants was studied on nitrile metabolizing enzyme from Amycolatopsis sp. IITR215 in which sorbitol proved to be an efficient lyoprotectant. In physical and mechanical methods, only 30% activity was recovered while 85% activity was achieved in the enzymatic method using 2 g/l lysozyme. Very less activity was recovered during stationary phase when cells were grown in mineral base media containing 1 g/l yeast. Therefore, recovery of intracellular enzymes was enhanced by using different concentrations of sodium cholate and deoxycholate.     

Photosynthesis in Cuscuta Reflexa: A Total Plant Parasite

Photosynthetic properties of Cuscuta species, such as chloroplast ultrastructure, contents of chlorophylls, carotenoids, and plastid proteins, photosystem and CO₂ fixation activities, and photosynthetic genes composition are reviewed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Nonspecific esterase isozymes that focus at identical isoelectric points are kinetically analogous

Isoelectric focusing (IEF) of soluble nonspecific esterases of rat kidney and testis exhibits an identical array of organophosphate-resistant cathodal isozymes. To ascertain whether such isozymes that focus at the same pI are also kinetically analogous, two isozymes, both focused at pI 7.2, were isolated, one from each organ, by elution from cut-out, unstained gel segments. Although the esterases of the whole soluble fraction of kidney and testis exhibited different kinetic properties and organophosphate susceptibility, no differences were observed with regard to the isozymes. Therefore, because of similar electrophoretic and kinetic behavior, the two isozymes can be regarded as phenotypic expressions of similar genetic products.     

A prospective study on correlation between the decrease in anti-P17 antibody level and progression to AIDS in asymptomatic carriers of HIV.

As the majority of human immunodeficiency virus (HIV) carriers are in asymptomatic stage for a long period of time, it is important to investigate the factors or surrogate markers for conversion from asymptomatic to symptomatic stage. Our study is designed to evaluate the relationship among virus isolation rate, anti-p17 antibody status and progression to AIDS. We studied anti-p17 antibody status along with virus isolation in 56 asymptomatic carriers and 46 AIDS cases. Progression to AIDS was markedly associated with high rate of virus isolation and loss of anti-p17 antibody. In order to know the meaning of loss of anti-p17 antibody during the clinical course, 15 anti-p17 antibody positive and 16 anti-p17 antibody negative cases were followed up prospectively for the development of AIDS. None of the anti-p17 antibody positive cases developed AIDS while 6 out of 16 anti-p17 negative cases developed AIDS during observation period (P < 0.05). Progression to AIDS was associated with loss of anti-p17 antibody. Identification of cases losing anti-p17 antibody in peripheral blood during asymptomatic period may help high-risk group who are in need of chemoprophylaxis. Moreover, study of anti-p17 antibody may be helpful in designing vaccine in future if it works as a neutralizing antibody to HIV in vivo.     

Population dynamics of hoolock gibbons (Hylobates hoolock) in Assam,India

Data are presented on group size, composition, and reproduction of several hoolock gibbon groups studied in different areas of Assam, India, between 1986 and 1988. Presence of fewer young than reported in earlier studies signals a grim future for these gibbons unless strict conservation measures are undertaken.     

In silico APC/C substrate discovery reveals cell cycle-dependent degradation of UHRF1 and other chromatin regulators

The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase and critical regulator of cell cycle progression. Despite its vital role, it has remained challenging to globally map APC/C substrates. By combining orthogonal features of known substrates, we predicted APC/C substrates in silico. This analysis identified many known substrates and suggested numerous candidates. Unexpectedly, chromatin regulatory proteins are enriched among putative substrates, and we show experimentally that several chromatin proteins bind APC/C, oscillate during the cell cycle, and are degraded following APC/C activation, consistent with being direct APC/C substrates. Additional analysis revealed detailed mechanisms of ubiquitylation for UHRF1, a key chromatin regulator involved in histone ubiquitylation and DNA methylation maintenance. Disrupting UHRF1 degradation at mitotic exit accelerates G1-phase cell cycle progression and perturbs global DNA methylation patterning in the genome. We conclude that APC/C coordinates crosstalk between cell cycle and chromatin regulatory proteins. This has potential consequences in normal cell physiology, where the chromatin environment changes depending on proliferative state, as well as in disease.

This study shows that the cell cycle E3 ubiquitin ligase APC/C is a regulator of several chromatin regulatory proteins, including the multivalent epigenetic reader and writer UHRF1. Perturbing UHRF1 ubiquitylation and degradation alters cell cycle and DNA methylation patterning, pointing to a key role for cell cycle degradation in shaping chromatin environments.     

In vivo analysis of trypanosome mitochondrial RNA function by artificial site-specific RNA endonuclease-mediated knockdown

Trypanosomes possess a unique mitochondrial genome called the kinetoplast DNA (kDNA). Many kDNA genes encode pre-mRNAs that must undergo guide RNA-directed editing. In addition, alternative mRNA editing gives rise to diverse mRNAs and several kDNA genes encode open reading frames of unknown function. To better understand the mechanism of RNA editing and the function of mitochondrial RNAs in trypanosomes, we have developed a reverse genetic approach using artificial site-specific RNA endonucleases (ASREs) to directly silence kDNA-encoded genes. The RNA-binding domain of an ASRE can be programmed to recognize unique 8-nucleotide sequences, allowing the design of ASREs to cleave any target RNA. Utilizing an ASRE containing a mitochondrial localization signal, we targeted the extensively edited mitochondrial mRNA for the subunit A6 of the F₀F₁ ATP synthase (A6) in the procyclic stage of Trypanosoma brucei. This developmental stage, found in the midgut of the insect vector, relies on mitochondrial oxidative phosphorylation for ATP production with A6 forming the critical proton half channel across the inner mitochondrial membrane. Expression of an A6-targeted ASRE in procyclic trypanosomes resulted in a 50% reduction in A6 mRNA levels after 24 h, a time-dependent decrease in mitochondrial membrane potential (ΔΨm), and growth arrest. Expression of the A6-ASRE, lacking the mitochondrial localization signal, showed no significant growth defect. The development of the A6-ASRE allowed the first in vivo functional analysis of an edited mitochondrial mRNA in T. brucei and provides a critical new tool to study mitochondrial RNA biology in trypanosomes.