The majority of the seed storage proteins of oats (Avena sativa L.), unlike those of most other cereals, are globulins [ 1,2]. The major globulin component has a sedimentation coefficient (~0,~) of 12.1 and a molecular weight (MI) of 320 000 and is thought to consist of six subunits of M, 21 700 and six of Mr 31 700 [3]. In many regards the major oat globulin resembles legumin, one of the two major seed storage proteins of legumes. Legumins from different species have qu,,-values of 11 to 14, Mrvalues of around 350 000 and consist of 6a and 6j3 subunits with M,-values of 22 000 and 37 000 respectively [4]. The amino acid composition of oat globulin [3] falls within the range of values reported for legumins [4]. The (Y and /3 subunits of legumin exist as dimers stabilized by disulphide bonds [4] and are synthesized in vitro and in vivo as a single 60 000 Mr precursor which undergoes post-translational processing in vivo to produce the individual subunit polypeptide chains [5-71. There is no evidence that the two types of oat globulin subunits associate as a disulphide stabilized dimer and it has been reported that the individual subunits are synthesized in vitro [8]. This paper reports that the oat globulin subunits are associated as dimers, of M, about 58 000, which can be dissociated into subunits upon reduction. We also show that polysomes isolated from developing endosperms direct the synthesis of a protein of M, about 58 000-60 000 which is specifically precipitated by oat globulin antiserum. Globulin In vitro translation
