Cloning, Sequence Analysis, andExpression ofa cDNA Encoding a Plastid-Localize d HeatShockProtein inMaize1

We havecloned andcharacterized acDNAencoding amaize (ZeamaysL.)heatshockprotein (HSP), HSP26.ThemRNA of HSP26ispresent asasingle mRNAspecies of1.1kilobase pairs insizeandisdetectable whenmaizeseedlings aretreated at 40°Cbutnotat280C. Accumulation ofHSP26mRNAwasdetected after 10minutes ofincubation at400C, reaching themaximum level after 1hour. Comparison ofthededucedaminoacidsequenceofmaizeHSP26toother HSPsindicated astrong homologytothesequences oftwonuclear encodedHSPsthatare transported into thechloroplasts during heatshock: peaHSP21 andsoybean HSP22. MaizeHSP26wasalsofound tocross-react withanti-pea chloroplast HSP21antibodies. Because ofthesequencehomology between maizeHSP26, soybean HSP22, and peaHSP21, invitro chloroplast protein import experiments were conducted. Theinvitro synthesized maizeHSP26isspecifically imported tothesoluble fraction ofthechloroplast andprocessed toasmaller polypeptide. Thesequence homology andantibody cross-reactivity between maizeHSP26andpeaHSP21haveallowedustoconclude thatmaizeHSP26isanuclear-encoded, plastid-localized protein inmaize.