Recruitment of RXR by homotetrameric
RARalpha fusion proteins is essential for transformation.
Cysteine biosynthesis is catalyzed by a bifunctional complex composed of two molecules of homodimeric O-acetylserine sulfhydrase and one molecule of homotetrameric
serine acetyl-transferase (Droux et al., 1998).
CAT, which catalyzes the conversion of [H.sub.2][O.sub.2] into water and oxygen, is a homotetrameric
protein containing four iron heme and largely located in the peroxisomes.
1C), indicating the oligomeric nature of insect PRIP subfamily members and suggesting the presence of a homotetrameric
AQP-Bom3 in vitellogenic and choriogenic ovaries.
In regard to membrane trafficking of AMPA receptors, the induction mechanism for LTP in hippocampal CA1 pyramidal neurons  includes increased incorporation of GluA1/GluA2-containing AMPA receptors into the synaptic surface membrane [62, 109]; however, subsequent work suggests that the newly incorporated AMPA receptors are in fact homotetrameric
GluA1 complexes .
The active enzyme has a homotetrameric
RyRs assemble as very large homotetrameric
structures with a molecular weight > 2 MDa and consist of a very large cytoplasmic assembly (the foot region) and a relatively small transmembrane assembly composed of six putative transmembrane passes with a central ion-conducting pore.