A primary transcript in spinach chloroplasts that completely lacks a 5' untranslated leader region.

A fifth, previously undetected transcript for the plastid gene encoding the beta subunit of spinach chloroplast ATPase (atpB) has recently been identified in vitro. In this report we show that this transcript is present in vivo and its 5' end is at the translation start codon. When synthesized in vitro using spinach chloroplast RNA polymerase, the 5' end of this novel transcript is located at the beginning of the second codon of the atpB coding sequence. Although this atpB transcript lacks an untranslated leader region, it is an abundant RNA in vivo and is associated with crude polysomal fractions, as are the four larger atpB transcripts. In vitro synthesis of the leaderless transcript does not occur for a plasmid DNA in which the "-35' region of the promoter is deleted.