Abstract. In all eukaryotes, the peripheral endoplasmic reticulum (ER) branches out of the nuclear envelope as a membrane network of interconnected tubules and membrane sheets with a single lumen. In yeast, Rtn1p and Yop1p are major, redundant components required to maintain the tubular ER under normal circumstances. In this work, we have investigated the homolog of the yeast Yop1 protein in Monascus purpureus. An M. purpureus cDNA library was constructed, and the MpYop1 cDNA was isolated from the cDNA library by random sequencing method. The cDNA was 1008 bp in length, contains a predicted 516 bp ORF that encodes 171 amino acids, the gene was designated MpYop1. The deduced amino acid sequence showed homology to Yop1 from fungi. The TM topology model of MpYop1 was built, the secondary structure is similar to yeast Yop1p. MpYop1 contains four transmembrane α-helices connected by a cytoplasmic loop and two extracellar loop, both the N and C termini are located in the cytoplasm side of ER membrane. According to functions of Yop1 in Yeast, we implicated that the MpYop1 would involved in stabilization of tubule ER. IntroductionThe endoplasmic reticulum (ER) is a continuous membrane system which has many different functions. These include the translocation of proteins across the ER membrane; the folding and modification of proteins in the ER lumen; the synthesis of phospholipids and steroids on the cytosolic side of the ER membrane; and the storage of calcium ions in the ER lumen and their regulated release into the cytosol [1][2]. ER is often tightly associated with almost every other membrane-bound compartment in the cell including the plasma membrane, nuclear envelope, mitochondria, golgi, vacuoles and peroxisomes. Interactions between these organelles have shown to be functionally important [3].The ER consists of the nuclear envelope and a peripheral network of tubules and membrane sheets. Peripheral ER sheets with little curvature except at their edges and the nuclear envelope with low curvature except where the nuclear pores are inserted. The ER is composed of a network of "rough," ribosome-studded sheets and smooth tubules that are continuous with the nuclear envelope. These subdomains are plastic and are remodeled in response to the needs of the cell. During interphase, enhanced protein synthesis and secretion promote morphology rich in sheets and rough ER, whereas lipid and steroid synthesis and detoxification promote abundant tubular smooth ER [4].The mechanism of ER network formation and maintenance is unclear. The possible model is based on mechanisms that generate or stabilize high curvature in membranes. Two protein families, the reticulons (Rtns) and DP1/Yop1 (Yip one partner), have been shown to shape the membrane bilayer of ER tubules in multiple eukaryotes, including animals, plants, and yeast [5][6]. Members of both families are ubiquitously expressed in all eukaryotic cells. In yeast, Rtn1p (one of reticulons) and Yop1p are most abundant membrane proteins [7]. Yeast lacking both reticulons and Yop1...
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