SulA protein, a cell division inhibitor in Escherichia coli, is degraded by Lon protease. The C-terminal eight residues of SulA have been shown to be recognized by Lon; however, it remains to be elucidated which amino acid in the C-terminus of SulA is critical for the recognition of SulA by Lon. To clarify this point, we constructed mutants of SulA with changes in the C-terminal residues, and examined the accumulation and stability of the resulting mutant SulA proteins in vivo. Substitution of the extreme C-terminal histidine residue with another amino acid led to marked accumulation and high stability of SulA in lon+ cells. A SulA mutant in which the C-terminal eight residues were deleted (SulAC161) showed high accumulation and stability, but the addition of histidine to the C-terminus of SulAC161 (SulAC161+H) made it labile. Similarly, SulAC161+H fused to maltose-binding protein (MBP–SulAC161+H) formed a tight complex with and was degraded rapidly by Lon in vitro. Histidine competitively inhibited the degradation of MBP–SulA by Lon, while other amino acids did not. These results suggest that the histidine residue at the extreme C-terminus of SulA is recognized specifically by Lon, leading to a high-affinity interaction between SulA and Lon.
This paper describes a very simple formulation of the reactor kinetic equation for arbitrary reactivity variations which can be solved analytically. The method of matched asymptotic expan• sions, which is a generalization of methods used in boundary-layer analysis, is employed to estimate the neutron density and the reactor period for ramp and periodic inputs. The small amounts of error arising in individual cases are analyzed quantitatively by comparison with results obtained from difference approximation (Runge-Kutta-Merson method). The validity of the zero-prompt-lifetime approximation and the stability condition for periodic inputs are also discussed. It is confirmed that the results obtained by the present method are numerically in com~le~e agree~ent with those by other ~~thods, provided the magnitudes of bias reactivity 1 pol, react1v1ty am ph tude I p 1 l and ramp reactlVIty I rt I are all very small compared with f3, that the angular frequency m
This paper describes a very simple formulation of the reactor kinetic equation for arbitrary reactivity variations which can be solved analytically. The method of matched asymptotic expan· sions, which is a generalization of methods used in boundary-layer analysis, is employed to estimate the neutron density and the reactor period for ramp and periodic inputs. The small amounts of error arising in individual cases are analyzed quantitatively by comparison with results obtained from difference approximation (Runge-Kutta-Merson method). The validity of the zero-prompt-lifetime approximation and the stability condition for periodic inputs are also discussed. It is confirmed that the results obtained by the present method are numerically in com~le~e agree~ent with those by other ~~thods, provided the magnitudes of bias reactivity 1 pol, react1v1ty am ph tude I p 1 l and ramp reactlVIty I rt I are all very small compared with f3, that the angular frequency m
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