When this mutant subunit is expressed in cells with wild-type α and β subunits it produces non-functional receptors. Since wild-type α and β subunits expressed alone are able to produce GABA inducible current this indicates that the mutation either prevents both coassembly of the mutant and wild-type subunits but also coassembly of the wild-type α and β subunits or prevents proper trafficking of the formed receptor to the membrane. Fusion of GFP onto this mutated subunit has indicated that it is localized to the endoplasmic reticulum instead of the cell membrane. As with other known GEFS+ type 3 mutation, Q351X likely results in neuronal hyperexcitability. SCN2A mutations
The final type of GEFS+ is caused by mutations in the SCN2A gene, which encodes a sodium channel α subunit. The first associated mutation in this gene is R187W, located on the intracellular region linking membrane spanning units two and three in the first domain (D1S2-S3, figure 3). Patients with this mutation have both febrile and afebrile seizures. Electrophysiological examination of this mutant revealed that it increases the time constant for inactivation, presumably increasing sodium current and leading to hyperexcitability. However, this mutation also yields channels that inactivate at more hyperpolarized potentials relative to wild-type channels, indicative of hypoexcitability. Whether the result on membrane excitability of this mutation is hyperexcitability or hypoexcitability is, as yet, unclear.The second known mutation in SCN2A associated with GEFS+ is R102X. This mutation is located in the intracellular N-terminus (figure 3) and results in SMEI in patients.
This is due to the observation that 3 amino-acid analogues converted into AHBA in cell-free extracts of  A. mediterranei. The rif cluster is responsible for the biosynthesis of rifamycins. It contains genes rifG through rifN, which were shown to biosynthesize AHBA. [10]  RifK, rifL, rifM, and rifN are believed to act as transaminases in order to form the AHBA precursor kanosamine. "RifH" encodes aminoDAHP synthase that catalyzes the condensation between 1-deoxy-1-imino-d-erythrose 4-phosphate and phosphoenolpyruvate. RifA through rifE encode a type I polyketide synthase module, with the loading module being a non-ribosomal peptide synthetase. In all, rifA-E assemble a linear undecaketide and are followed by rifF, which encodes an amide synthase and causes the undecaketide to release and form a macrolactam structure. Moreover, the rif cluster contains various regulatory proteins and glycosylating genes that appear to be silent. Other types of genes seem to perform post-synthase modifications of the original polyketide. Derivatives
Lepetit introduced Rifampicin, an orally active rifamycin, around 1966. Rifabutin, a derivative of rifamycin S, was invented around 1975 and came onto the US market in 1993. Hoechst Marion Roussel (now part of Aventis) introduced rifapentine in 1999. Rifaximin is an oral rifamycin marketed in the US by Salix Pharmaceuticals that is poorly absorbed from the intestine. It has been used to treat hepatic encephalopathy and travelers diarrhea. Currently available rifamycins
Rifampicin or Rifampin
Rifabutin
Rifapentine
Rifaximin
Aemcolo

References
Bibliography
Sensi. et al., Farmaco Ed. Sci. (1959) 14, 146-147 - the paper announcing the discovery of the rifamycins. Thieman et al. Arch. Microbiol.