Can recA protein promote homologous pairing between duplex regions of DNA?

RecA protein has been shown to promote the formation of joint molecules between intact duplex DNA and homologous gapped DNA. When examined by electron microscopy, such joint molecules display a junction that is, in most cases, distant from the site of the gap. This led us to test whether the observed location of the joint was due to pairing at the gap followed by branch migration, or whether recA-promoted pairing could also take place between duplex homologous regions away from the gap. To test the latter possibility, intact duplex DNA was incubated with DNA which contained a gap in a region of non-homology. Joint molecules were detected by filter binding assay and by electron microscopy at about one-third of the yield observed for fully homologous molecules. These results indicate that initial homologous pairing promoted by recA protein is not restricted to the single-stranded region in the gap but can also take place in regions where both molecules are duplex.     

Hypothetical 92.3-kD human protein homologous to angiotensin-converting enzyme: a new member of the zinc metalloprotease family?

Significant identity between a hypothetical 92.3-kD human protein and angiotensin-converting enzyme (ACE; peptidyl-dipeptidase A; kininase II) has been found. Certain specific regions of the 92.3-kD protein indicate that this unidentified molecule may be a member of the zinc metalloprotease family. A method is suggested for determination of a structural and functional family of proteins with unknown structure and function.     

Virulence protein export systems in Salmonella and Shigella: a new family or lost relatives?

A number of Gram-negative bacterial pathogens secrete 'virulence determinants' directly into the extracellular medium, where they interact with host cells to promote disease. The study of the secretion machinery used by these organisms to transport specific virulence determinants out to the cell surface and beyond is of growing importance in the field of bacterial pathogenesis. Elements of the secretion machinery are shared by several pathogens. These homologous elements may lead to a better understanding of how the machinery works, but the unique elements will tell us more about what distinguishes one bacterial pathogen from another.     

Protein kinase C – A family of protein kinases, allosteric effectors or both?

The nucleotide dependence of PKC priming phosphorylations has provided compelling evidence for an ATP-induced conformational change to the kinase domain. This has various implications for the manner in which kinase inactive dominant negative PKC mutants work and also predicts that those inactivating mutations that do not lead to loss of priming may provide a more selective route to dominant negative mutants. It might be argued that this is also the case for other kinases and that caution should be employed in considering the dominant properties of the lysine mutant forms. In fact this pattern of behaviour is shared to some extent, with very clear examples of nucleotide pocket directed inhibitors triggering related phosphorylations and responses in other kinases. Alongside these cautionary tales, the functional implications for pseudokinases are clear, so that ATP binding within a suitably conserved nucleotide pocket can trigger conformational change and impact on the scaffolding function of that pseudokinase – here the kinase itself is simply an “ATP effector”.     

A novel UV laser-induced visible blue radiation from protein crystals and aggregates: scattering artifacts or fluorescence transitions of peptide electrons delocalized through hydrogen bonding?

Proteins lacking prosthetic groups and/or cofactors are known to undergo electronic excitation transitions only upon exposure to UV-C (< 280 nm) and UV-B (280-320 nm), but not UV-A (320-400 nm) photons. Here, we report the discovery of a novel excitation that peaks at approximately 340 nm and yields visible violet-blue radiation with apparent band maxima at approximately 425, 445, 470, and 500 nm. All proteins and large polypeptides examined in solid form, and in solutions, display this quenchable and photobleachable radiation which can be established not owing to aromatic sidechains. As a note of caution, we wish to state that we have not been able to completely eliminate the possibility that the radiation may be an artifact owing to second order effects such as, e.g., Raman scattering of Raman-scattered photons; however, we assert that all our experiments indicate that the radiation actually owes to some form of fluorescence. We propose that peptide electrons that have been delocalized through intramolecular or intermolecular hydrogen bond formation display these long-wavelength electronic transitions. If confirmed by future studies, this preliminary discovery may turn out to have important implications for biomolecular spectroscopy, protein crystallography, and materials science.