Fig. 8. A model for regulation of Cox1p synthesis based on its physical interaction with Mss51p. This model is based on the possibility that the target specified by the COX1 coding sequence, through which Mss51p promotes Cox1p synthesis, is Cox1p itself. We propose the following. (A) Translation elongation of the COX1 mRNA (green line) may be arrested by interaction of the nascent Cox1p polypeptide (black, thick line) with the ribosome. (B) Interaction of Mss51p with nascent Cox1p allows completed translation. (C) Mss51p ‘hands off’ newly synthesized Cox1p to Shy1p, and possibly other proteins, for assembly. Mss51p is then released and available to interact with another Cox1p nascent polypeptide as shown in (A). The mitochondrial inner membrane is shown as a brown bar. For simplicity, the action of Mss51p through the COX1 mRNA UTRs to promote translation was not included in this model, since the target could involve the COX1 5′-UTR, the 3′-UTR or both.