Introduction

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Introduction

Nucleotide binding protein 2 is a novel protein defined which represent the eukaryotic nucleotide binding protein family. NUBP2 represent the short form of nucleotide binding protein which belongs to the partitioning ATPase gene family. The protein from this family function by drawing energy from hydrolysis of ATP, and they share a characteristic sequence motif of “[GA]-X2-(G)-X-G-K-[ST],” called the “phosphate-binding loop (P-loop)” (Walker et al., 1982; Saraste et al., 1990). Although the structure of NUBP2 is not completely solved, but the high similarity of NUBP2 with 2ph1 (MinD homologue, E.coli) make the function analysis possible. E.coli MinD was also included in the Partitioning ATPase gene family, it is a membrane associated ATPase which inhibits the cell division at the poles and consequently induces normal cell division (de Boer et al., 1991), and based on sequence similarity, the E. coli mrp gene (Dardel et al., 1990). The similarity between 2ph1 and NUBP2 is about 39.66% of the sequence, and by using the structure of 2ph1, the function of NUBP2 would be analysed based on the structure searching. The division septum is normally placed at the midpoint of the cell, but potential division sites also exist near each of the cell poles. Restriction of the cell division site at the midpoint is governed by the product of the three genes of the MinB operon, MinC, MinD and MinE. MinC inhibits the division at all of the potential division sites and requires the activity of peripheral membrane ATPase MinD for its function. MinC and MinD act cooperatively to form a non-specific division inhibitor complex. MinE has two functions: it suppresses the MinCD-mediated division inhibition and recognizes the mid-cell point from the cell poles. In order words, MinE promotes mid-cell division by excluding MinCD from the mid-cell site. Based on the homology similarity of NUBP2 to E. coli MinD protein, we hypothesed that NUBP2 involves in cell division to determine the position of septum (Z-ring). Another function of this protein is hydrolyse ATP molecules in cell. Further analysis was conducted in structural study on NUBP2 to deduce the function of NUBP2 protein.