pET-27b質(zhì)粒是一種原核表達載體，C端含有一個6×His標簽、HSV標簽，N端含有一個pelB前導肽。該質(zhì)粒含有多個常用的酶切位點，便于不同基因克隆。表達由宿主細胞提供的T7 RNA聚合酶誘導，目的基因被克隆到質(zhì)粒載體上，受噬菌體強轉錄及翻譯信號控制。
pET系統(tǒng)是有史以來在大腸桿菌中表達重組蛋白的功能*強大的系統(tǒng)，也是現(xiàn)今原核表達方面使用*廣泛的系統(tǒng)。該系列質(zhì)粒能很容易的通過降低誘導物的濃度來削弱蛋白表達。在非誘導條件下，可以使目的基因處于完全沉默狀態(tài)而不轉錄。
The pET-27b(+) vector carries an N-terminal pelB signal sequence for potential periplasmic localization, plus optional C-terminal HSV?Tag® and His?Tag® sequences. This vector differs from pET-25b(+) only by its selectable marker (kanamycin vs. ampicillin resistance).Unique sites are shown on the circle map. Note that the sequence is numbered by the pBR322 convention, so the T7 expression region is reversed on the circular map. The cloning/expression region of the coding strand transcribed by T7 RNA polymerase is shown below. The f1 origin is oriented so that infection with helper phage will produce virions containing single-stranded DNA that corresponds to the coding strand. Therefore, single-stranded sequencing should be performed using the T7 terminator primer .