9.B.323. The Putative ABC3 Auxiliary Protein (ABC3-AP) Family The proteins of this family usually have two TMSs, one N-terminal, and one C-terminal. Many but by no means all of them cluster with complete ABC3-type transport systems, most in archaea, but also many in firmicutes and actinobacteria (see several ABC3 system listed under TC# 3.A.1.122). They have a wide range of sizes, from about 300 to about 1000 aas. They are more sequence divergent than the membrane proteins of the ABC3 systems with which they possibly function. The genes for the putative auxiliary proteins are often in an operon together with the membrane exporter and the ATPase, with the auxililary protein encoded by the middle gene. This is the COG1361 family. Some of these proteins are annotated as 'S-layer proteins' or 'ABC transporter' or 'exo-alpha-silalidase' in the NCBI database.
Examples:
TC#	Name	Organismal Type	Example
9.B.323.1.1	Putative auxiliary protein of ABC3 export systems of 626aas and 1 C-terminal TMSs.		Putative auxiliary protein of Haloarcula argentinensis

9.B.323.1.2	Putative ABC3 auxiliary protein of 495 aas and 2 TMSs, one N-terminal and one C-terminal.		*Auxiliary protein of Robinsoniella* sp. MCWD5**

9.B.323.1.3	Uncharacterized protein of 900 aas and 2 TMSs, N- and C-terminal.		UP of Thermococcus litoralis

9.B.323.1.4	S-layer protein of 541 aas and 1 N-terminal TMS		S-layer protein of Archaeoglobales archaeon (marine sediment metagenome)

9.B.323.1.5	Uncharacterized putative carboxyl-terminal-processing protease of 511 aas and 2 TMSs, one near the N-terminus and the other at the C-terminus.		*Uncharacterized protein of Methanosarcina* sp. Kolksee**

9.B.323.1.6	Uncharacterized protein of 499 aas and 2 TMSs, N- and C-terminal.		UP of Haloquadratum walsbyi

Examples:
TC#	Name	Organismal Type	Example
9.B.323.2.1	Uncharacterized protein of 692 aas and 2 TMSs, one N-terminal and one C-terminal.		UP of Saccharolobus solfataricus (Sulfolobus solfataricus)

Examples:
TC#	Name	Organismal Type	Example
9.B.323.3.1	Uncharacterized protein of 1331 aas and 2 TMSs, N- and C-terminal. This protein is encoded by a gene adjacent to an ABC3-type exporter with TC# 3.A.1.207.7. It may be an auxiliary subunit of this ABC exporter.		UP of Candidatus Lokiarchaeota archaeon (marine sediment metagenome)