41,304 research outputs found
Cloning and expression of first gene for biodegrading microcystins by Sphingopyxis sp. USTB-05
Harmful cyanobacterial blooms (HCBs) in natural waters are a growing environmental problem worldwide because microcystins (MCs) produced by cyanobacteria are potent hepatotoxins and tumor promoters. MCs are resistant against physical and chemical factors. Thus, biodegradation is the most efficient method for removing MCs, and a number of bacterial strains, especially genus _Sphingomonas_, have been isolated for biodegrading MCs. Although the pathway, enzyme, and gene for biodegrading MCs by _Sphingomonas sp._ have been widely identified recently, no gene concerned with the biodegradation of MCs has been successfully cloned and expressed. In this study, we show that the first and most important gene of mlrA, containing 1,008 bp nucleotides in length, in the biodegradation pathway of MCs by _Sphingopyxis sp._ USTB-05, which encodes an enzyme MlrA containing 336 amino acid residues, is firstly cloned and expressed in _E. coli_ DH5α, with a cloning vector of pGEM-T easy and an expression vector of pGEX-4T-1. The encoded and expressed enzyme MlrA is responsible for cleaving the target peptide bond between 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyl-deca-4,6-dienoic acid (Adda) and Arg in the cyclic structure of microcystin-RR (MC-RR)and microcystin-LR(MC-LR), two typical and toxic types of MCs. Linear MC-RR and MC-LR are produced as the first products. These findings are important in constructing a new genetic bacterial strain for the efficient removal of MCs from the important water supplies and resolving the controversy on the biodegradation pathway of different types of MCs by genus _Sphingomonas_
Antifactors of regular bipartite graphs
Let be a bipartite graph, where and are color classes and
is the set of edges of . Lov\'asz and Plummer \cite{LoPl86} asked
whether one can decide in polynomial time that a given bipartite graph admits a 1-anti-factor, that is subset of such that for
all and for all . Cornu\'ejols \cite{CHP}
answered this question in the affirmative. Yu and Liu \cite{YL09} asked
whether, for a given integer , every -regular bipartite graph
contains a 1-anti-factor. This paper answers this question in the affirmative
Generalizations of Ramanujan's reciprocity formula and the Askey-Wilson integral
By using two known transformation formulas for basic hypergeometric series,
we establish a direct extension of Bailey's -series identity.
Subsequently, it and Milne's identity are employed to drive multi-variable
generalizations of Ramanujan's reciprocity formula. Then we utilize also
Milne's identity to deduce a multi-variable generalization of the Askey-Wilson
integral
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