Charged residues in the cytoplasmic loop of MotA are required for stator assembly into the bacterial flagellar motor

MotA and MotB form a transmembrane proton channel that acts as the stator of the bacterial flagellar motor to couple proton flow with torque generation. The C-terminal periplasmic domain of MotB plays a role in anchoring the stators to the motor. However, it remains unclear where their initial binding sites are. Here, we constructed Salmonella strains expressing GFP-MotB and MotA-mCherry and investigated their subcellular localization by fluorescence microscopy. Neither the D33N and D33A mutations in MotB, which abolish the proton flow, nor depletion of proton motive force affected the assembly of GFP-MotB into the motor, indicating that the proton translocation activity is not required for stator assembly. Overexpression of MotA markedly inhibited wild-type motility, and it was due to the reduction in the number of functional stators. Consistently, MotA-mCherry was observed to colocalize with GFP-FliG even in the absence of MotB. These results suggest that MotA alone can be installed into the motor. The R90E and E98K mutations in the cytoplasmic loop of MotA (MotA(C) ), which has been shown to abolish the interaction with FliG, significantly affected stator assembly, suggesting that the electrostatic interaction of MotA(C) with FliG is required for the efficient assembly of the stators around the rotor.     

Stability of rRNA genes during germination of Vicia faba seeds

Germinating Vicia embryos and the roots of 4-day-old seedlingswere assayed for the proportion of DNA that is complementaryto Vicia rRNA. Hybridization experiments which were performedusing DNA purified by ordinary procedures including RNase digestionshowed a higher level of saturation only for the DNA from theembryos. The embryo DNA showed a Tm of 74?C in 0.1?SSC, whereasthe Tm of the root DNA was 70?C. However, our final conclusionis that there is no gross amplification of rRNA genes for Viciafaba, since the saturation level for the embryo DNA did notexceed that for the root DNA when the DNAs were used after additionalpurification on CsCl gradients. ¹ Present address: Department of Botany, Faculty of Education,Utsunomiya University, Utsunomiya 320, Japan. (Received November 25, 1974; )     

An Improved Method for Determining the Ionic Conductance and Capacitance of the Membrane of Chara corallina

The assumption of a single exponential change for the voltageresponse caused by a square current of subthreshold intensityis not necessarily an adequate explanation of the situationin the Chara membrane. By improving the speed of electronicsfor current clamping and the accuracy of data simulation, itwas found that an additional process, which can be generallysimulated with another exponential function, was superimposedon the voltage response. Such an additional exponential processmay be partly atributed to the response of the tonoplast, ifthe internal potential measuring microelectrode is in the vacuole.However, this additional process still remained in the voltageresponse of the plasmalemma of the Chara internode when thetonoplast and a large amount of endoplasm were removed by internalperfusion with an glycol ether diaminetetraacetic acid solution.The additional exponential component arose from the change ofthe electromotive force of the single membrane during applicationof the test current pulse. The increase of the conductance of the plasmalemma alone waslarge during excitation, while that of the elecrostatic capacitancewas negligible. On the other hand, the conductance and capacitancewhich reflect an additional exponential ionic process duringthe test pulse both increased greatly around the peak of excitation.This rise is the main reason for an apparent large increaseof membrane capacitance which was deduced from a simple approximationof the membrane with a single time constant model. (Received January 6, 1982; Accepted June 23, 1982)