*3.1. The Structure of TRIOBP-4*

Human TRIOBP-4 is a 1144 amino acid long protein, which is predicted to be almost entirely disordered, possessing no fixed secondary or tertiary structure [49]. While TRIOBP-4 therefore possesses no folded domains, it has been observed to contain two repeat regions [4], referred to as R1 and R2 (Figure 4a) [49]. The R1 repeat region lies near the center of the protein. In humans, it has a high isoelectic point of 11.7 and consists of six repeats (with slight variations) of the sequence SSPNRTTQRDNPRTPCAQRDNPRA [49]. R2, in humans, consists of five repeats of the sequence VCIGHRDAPRASSPPR (with slight variations), with 30–40 amino acids between each repeat. It lies in the C-terminal half of TRIOBP-4 and has a much lower isoelectric point of 5.4 [49].

**Figure 4.** (**a**) The location of the repeats that make up the R1 and R2 regions of TRIOBP-4, with ¸amino acid numbering of both TRIOBP-4/5 and TRIOBP-6. (**b**) The location of frameshift and nonsense mutations from patients with hearing loss. Red bars indicate homozygous mutations, while purple bars joined by dotted lines indicate compound heterozygous mutations. Arrowheads indicate that the other heterozygous mutations lie in a region of *TRIOBP-5*/*6* that is 3 ′ of the *TRIOBP-4* open reading frame. Full details of these are in Table 1. All elements of this figure are shown to scale.
