Reticulocalbin (RTC)

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Reticulocalbin (RTC), also known as E6BP (E6 binding protein) or ERC-55, appears to bind E6, a transforming protein from human papilloma virus that interacts with tumor suppressor protein p53. RTC has 210 amino acids [27]. It contains six EF-hands, several of which are most similar to the corresponding domains of SCF. RTC is inferred to be in the lumen of the endoplasmic reticulum because it has an N-terminal leader sequence and a glycosylation site. The C-terminal sequence is HDEL; this is similar to the KDEL that serves as a signal to retain proteins within the ER. Four of six EF-hands (1, 4, 5 & 6) bind calcium but 2 & 3 do not [28].