Human liver RNA‐programmed in vitro synthesis of a polypeptide related to human apolipoprotein B

In an in vitro synthesizing system programmed with RNA from human liver a polypeptide with an estimated Mr of 80 000 (80 kDa) +/- 1400 (mean +/- SD, n = 5) was synthesized. This polypeptide could be precipitated with antiserum to a narrow density cut of LDL (d = 1.030-1.055) or antiserum against the high-Mr form of apoB (apoB 100 [4]). The synthesized protein is immunologically related to a 75 kDa protein isolated from LDL. We suggest that the 80 kDa protein represents a primary translation product of apoB synthesized in human liver.