Forkhead-associated domains of the tobacco NtFHA1 transcription activator and the yeast Fhl1 forkhead transcription factor are functionally conserved.
NtFHA1 encodes a novel protein containing the forkhead-associated (FHA) domain and the acidic domain in Nicotiana tabacum. NtFHA1 functions as a transactivator and is targeted to the nucleus. The sequence of the FHA domain of NtFHA1 is significantly homologous to that of the Fhl1 forkhead transcription factor of yeast. FHL1 was previously identified as a suppressor of RNA polymerase III mutations, and the fhl1 deletion mutant exhibited severe growth defects and impaired rRNA processing. Ectopic expression of the FHA domain of NtFHA1 (but not its mutant form) resulted in severe growth retardation in yeast. Similarly, expression of Fhl1, its FHA domain, or chimeric Fhl1 containing the NtFHA1 FHA domain also inhibited yeast growth. Yeast cells overexpressing the FHA domains of NtFHA1 and Fhl1 contained lower levels of mature rRNAs and exhibited rRNA-processing defects, similar to the fhl1 null mutant. Chimeric Fhl1 (but not the mutant form with a small deletion in its FHA domain) fully complemented the growth and rRNA-processing defects of the fhl1 null mutant, demonstrating that the FHA domain of NtFHA1 can functionally substitute for the FHA domain of Fhl1. These results demonstrate that the FHA domains of NtFHA1 and Fhl1 are conserved in their structure and function and that the FHA domain of Fhl1 is critically involved in regulation of rRNA processing in yeast. NtFHA1 function in plants may be analogous to Fhl1 function in yeast.
Kim
Moonil
M
Laboratory of Plant Genomics, Korea Research Institute of Bioscience and Biotechnology, Yusong, Taejon 305-333, Korea.
Ahn
Joon-Woo
JW
Song
Kiwon
K
Paek
Kyung-Hee
KH
Pai
Hyun-Sook
HS
D000595:Amino Acid Sequence; D002453:Cell Cycle / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D005434:Flow Cytometry; D051858:Forkhead Transcription Factors; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012335:RNA, Ribosomal / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D016415:Sequence Alignment; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D051858:Forkhead Transcription Factors; D005656:Fungal Proteins; D009687:Nuclear Proteins; D010940:Plant Proteins; D012335:RNA, Ribosomal; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors