Isotype-specific changes in the amount of β-tubulin RNA in synchronized tobacco BY2 cells

The 3'-ends of the β-tubulin cDNA were amplified from tobacco BY2 polyA⁺ RNA. According to the differences in the predicted amino acid sequence at the extreme C-terminal, they were grouped into three different isotypes, NTB1 in which 'EEGDYYEEDEEDLNEA', NTB2 in which 'EEEYYEDEEEAQED' and NTB3 in which 'DECEYEEEEEYDHEGN' follows the conservative 'YQQYQDATAD' sequence. Using unique 3'-untranslated regions as probes, changes in the RNA levels of each β-tubulin isotype were determined by dot-blot hybridization. The levels exhibited characteristic rhythms in the cell cycle. NTB1 RNA was highest in S phase in comparison to NTB2 RNA level which was highest in late G2. On the other hand, NTB3 RNA level was highest in early G2.