PT  - JOURNAL ARTICLE
AU  - Gillikin, J. W.
AU  - Zhang, F.
AU  - Coleman, C. E.
AU  - Bass, H. W.
AU  - Larkins, B. A.
AU  - Boston, R. S.
TI  - A Defective Signal Peptide Tethers the floury-2 Zein to the Endoplasmic Reticulum Membrane
AID  - 10.1104/pp.114.1.345
DP  - 1997 May 01
TA  - Plant Physiology
PG  - 345--352
VI  - 114
IP  - 1
4099  - http://www.plantphysiol.org/content/114/1/345.short
4100  - http://www.plantphysiol.org/content/114/1/345.full
SO  - Plant Physiol.1997 May 01; 114
AB  - The maize (Zea mays L.) floury-2 (fl2) mutation is associated with a general decrease in storage protein synthesis, altered protein body morphology, and the synthesis of a novel 24-kD [alpha]-zein storage protein. Unlike storage proteins in normal kernels and the majority of storage proteins in fl2 kernels, the 24-kD [alpha]-zein contains a signal peptide that would normally be removed during protein synthesis and processing. The expected processing site of this [alpha]-zein reveals a putative mutation alaine->valine (Ala->Val) that is not found at other junctions between signal sequences and mature proteins. To investigate the impact of such a mutation on signal peptide cleavage, we have assayed the 24-kD fl2 [alpha]-zein in a co-translational processing system in vitro. Translation of RNA from fl2 kernels or synthetic RNA encoding the fl2 [alpha]-zein in the presence of microsomes yielded a 24-kD polypeptide. A normal signal peptide sequence, generated by site-directed mutagenesis, restored the capacity of the RNA to direct synthesis of a properly processed protein in a cell-free system. Both the fl2 [alpha]-zein and the fl2 [alpha]-zein (Val->Ala) were translocated into the lumen of the endoplasmic reticulum. The processed fl2 [alpha]-zein (Val->Ala) was localized in the soluble portion of the microsomes, whereas the fl2 [alpha]-zein co-fractionated with the microsomal membranes. By remaining anchored to protein body membranes during endosperm maturation, the fl2 zein may thus constrain storage protein packing and perturb protein body morphology.