"A tale of two membranes", "follow the (Spliced) Leader" and more in my picks of the week from RB

Another week has gone by and some very interesting molbio blog posts have been aggregated to Researchblogging.org. Every week [see my opening post on the matter], I'll select some blog posts I consider particularly interesting in the field of molecular biology [see here to get a sense of the criteria that will be used], briefly describe them and list them here for you to check out.

Note that I'm only taking into consideration the molbio-related blog posts aggregated under "Biology".

Congratulations to everyone who got their post selected.

1) Nitric oxide synthases are highly regulated heme-based enzymes that oxidize L-arginine to nitric oxide (NO) and L-citrulline. NO has been described as an important signaling molecule and cytotoxin in eukaryotes. Interestingly, bacteria can also produce NO from arginine thanks to a structurally and mechanistically related enzyme termed bacterial nitric oxide synthase (bNOS), which is present in many Gram-positive species. J. Kandler at "Blogging for Bacteriophages" discusses a recent article reporting a physiological role for bNOS. It appears that NO generated by bNOS "increases the resistance of bacteria to a broad spectrum of antibiotics through both the chemical modification of toxic compounds and the alleviation of oxidative stress".

2) Bacteria are commonly classified as either Gram-positive or Gram-negative according to their ability to retain a particular stain (crystal violet) after being washed with an organic solvent, which reflects differences in the composition of their cell walls. Gram-negative bacteria have two lipid membranes surrounding a thin peptidoglycan wall (and don’t retain the stain), while Gram-positive bacteria have a much larger peptidoglycan cell wall and lack an outer lipid membrane (and do retain the stain).

LabRat discusses a thought-provoking article supporting the position of the root “of the tree of all life” within the eubacteria, specifically with the Chlorobacteria (green non-sulfur) representing the earliest diverging eubacterial lineage. An interesting idea put forward in the article is that eubacteria with two membranes arose first, with those having only one membrane (like gram positive bacteria) evolving from them.

3) Spliced-leader (SL) trans-splicing is a nuclear RNA processing reaction where a small leader sequence, derived from an SL RNA, is attached to the most 5′ exon of an independently transcribed pre-mRNA. It was first discovered in trypanosomes, but was later shown to be present in dinoflagellates, cnidarians, rotifers, nematodes, flatworms and urochordates. SL trans-splicing has a patchy phylogenetic distribution and enigmatic evolutionary origins.

This patchy distribution poses an interesting question: is SL trans-splicing an ancestral eukaryotic trait that has been lost in multiple lineages or did it arise independently in the various groups where it occurs?
Lucas Brouwers at Thoughtomics comments on a recent article providing evidence for multiple independent origins of trans-splicing in Metazoa.


That's it for this week. Stay tuned for more MolBio Research Highlights!

---
Some of the articles discussed in this week's selected posts:

Gusarov I, Shatalin K, Starodubtseva M, & Nudler E (2009). Endogenous nitric oxide protects bacteria against a wide spectrum of antibiotics. Science (New York, N.Y.), 325 (5946), 1380-4 PMID: 19745150

Cavalier-Smith T (2006). Rooting the tree of life by transition analyses. Biology direct, 1 PMID: 16834776

Douris V, Telford MJ, & Averof M (2009). Evidence for multiple independent origins of trans-splicing in Metazoa. Molecular biology and evolution PMID: 19942614