Has a central role in coupling the hydrolysis of ATP to the transfer of proteins across the thylakoid membrane. Involved in photosynthetic acclimation and required for chloroplast biogenesis. ATP + H2O + chloroplast-proteinSide 1 = ADP + phosphate + chloroplast-proteinSide 2. Part of the Sec protein translocation apparatus. Interacts probably with SCY1. A minor fraction is associated with the chloroplast thylakoid membrane. A number of isoforms are produced. According to EST sequences. Expressed in green tissues, including cotyledons, rosette and cauline leaves, and sepals. Also detected at the base and the tip of the trichome. Induced steadily during photomorphogenesis. Up-regulated when light-grown seedlings are shifted to the dark. Seedling lethal. Albino seedlings with yellow and translucent (glassy) lateral organs when grown heterotrophically. Cannot substitute for SECA2. Belongs to the SecA family.