# Ribosome nascent chain complexes of the chloroplast-encoded cytochrome b6 thylakoid membrane protein interact with cpSRP54 but not with cpSecY

## TL;DR

This study explores how the cytochrome b6 protein interacts with specific factors during its production in chloroplasts.

## Contribution

The study reveals that cpSRP54 interacts with cytochrome b6 during translation, but cpSecY does not.

## Key findings

- The cytochrome b6 nascent chain is tightly associated with ribosomes during translation.
- Translation of cytochrome b6 is discontinuous, possibly aiding in proper folding and membrane insertion.
- cpSRP54 interacts with the elongating cytochrome b6 chain, but cpSecY does not.

## Abstract

We analysed the interplay between the cpSecY, cpSRP54 and the chloroplast-encoded cytochrome b6 via isolation of chloroplast ribosome nascent chain complexes and the use of cross-linking factors, antibodies and mass spectroscopy analyses. We showed that the cytochrome b6 nascent polypeptide complex is tightly associated with ribosomes and that the translation of cytochrome b6 was discontinuous. The causes of ribosome pausing and the functional significance of this phenomenon may be related to proper protein folding, insertion into thylakoid membranes and the association of cofactors during this process. It was also found that cpSecY was not in the vicinity of cytochrome b6 intermediates during the elongation process and does not act with mature cytochrome b6 after translation. Using the approach of cross-linking during elongation of the cytochrome b6 protein, we showed that cpSRP54 interacts strongly with the elongating nascent chain.

The online version of this article (doi:10.1007/s10863-014-9598-0) contains supplementary material, which is available to authorized users.