containing an RNA helicase can degrade highly structured RNA molecules. It has been reported that the rhlB gene can be deleted without lethal consequences 26. However, the putative deletion strain still has a copy of rhlB, and more recent attempts to delete the gene failed, indicating that rhlB may be essential (our unpublished results; M. Cashel, personal communication). The results reported here provide evidence of a DEAD-box RNA helicase having an active role in bacterial mRNA degradation. D
Calcium ions entering cells through voltage-gated Ca2+ channels initiate rapid release of neurotransmitters and secretion of hormones. Ca2+ currents can be inhibited in many cell types by neurotransmitters acting through G proteins via a membrane-delimited pathway independently of soluble intracellular messengers. Inhibition is typically caused by a positive shift in the voltage dependence and a slowing of channel activation and is relieved by strong depolarization resulting in facilitation of Ca2+ currents. This pathway regulates the activity of N-type and P/Q-type Ca2+ channels, which are localized in presynaptic terminals and participate in neurotransmitter release. Synaptic transmission is inhibited by neurotransmitters through this mechanism. G-protein alpha subunits confer specificity in receptor coupling, but it is not known whether the G alpha or G beta gamma subunits are responsible for modulation of Ca2+ channels. Here we report that G beta gamma subunits can modulate Ca2+ channels. Transfection of G beta gamma into cells expressing P/Q-type Ca2+ channels induces modulation like that caused by activation of G protein-coupled receptors, but G alpha subunits do not. Similarly, injection or expression of G beta gamma subunits in sympathetic ganglion neurons induces facilitation and occludes modulation of N-type channels by noradrenaline, but G alpha subunits do not. In both cases, the G gamma subunit is ineffective by itself, but overexpression of exogenous G beta subunits is sufficient to cause channel modulation.
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