Abstract
Proteins are translocated across the chloroplast thylakoid membrane by a variety of mechanisms. Some proteins engage a translocation machinery that is derived from the bacterial Sec export system and require an interaction with a chloroplast-localized SecA homologue. Other proteins engage a machinery that is SecA-independent, but requires a transmembrane pH gradient. Recently, a counterpart to this Delta pH mechanism was discovered in bacteria. Genetic studies revealed that one maize protein involved in this mechanism, HCF106, is related in both structure and function to the bacterial tatA and tatB gene products. We describe here the mutant phenotype and molecular cloning of a second maize gene that functions in the Delta pH mechanism. This gene, thylakoid assembly 4 (tha4), is required specifically for the translocation of proteins that engage the Delta pH pathway. The sequence of the tha4 gene product resembles those of the maize hcf106 gene and the bacterial tatA and tatB genes. Sequence comparisons suggest that tha4 more closely resembles tatA, and hcf106 more closely resembles tatB. These findings support the notion that this sec-independent translocation mechanism has been highly conserved during the evolution of eucaryotic organelles from bacterial endosymbionts.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.