These elements include three sequences: boxA, boxB and boxC which bind the cellular factors that construct the antitermination complex. These cellular 
factors include the Nus factors and several ribosomal proteins. The factors facilitate the interaction between the box elements, RNAP and Rho and secure the transcription antitermination process. The transcription antitermination process has two roles in addition to its primary function: to assist processing of the mature rrn transcript from the precursor state and to modulate the transcription elongation rate thus ensuring the proper folding of the rRNA. It is, therefore, clear that the transcriptional antitermination system is critical for several stages of ribosome biogenesis. Here we present evidence suggesting the involvement of a newly-analyzed protein YbeY in the transcription antitermination process. YbeY is a 17 kD heat shock protein that belongs to the addition chronic accumulation triggers reduction sst level UPF0054 family and is highly conserved in bacteria. Previous studies indicated that YbeY is important for translation and its absence results in production of impaired 30 S ribosomal subunits because of abnormal maturation of rRNA. Recently YbeY was shown to be a metallo endoribonuclease and with several functions including rRNA maturation and 70 S ribosome quality control. The results presented here indicate that YbeY has an additional role in transcriptional antitermination, that is critical for production of ribosomal subunits and could explain the defect in rRNA maturation. It has been shown that YbeY is essential for correct rRNA maturation, but the molecular basis of this effect has not been elucidated. One factor that could play a role in RNA maturation is the transcription antitermination process which is important for maintaining an optimal elongation rate for correct processing and folding of the RNA. YbeY is involved in ribosome biogenesis – in its absence ribosomes are defective and translation is reduced, especially at elevated temperatures. Here we show the involvement of YbeY in the transcriptional antitermination process of rRNA synthesis, which is critical for ribosome biogenesis. Thus, we show that YbeY is essential for rrn transcription of regions that contain the antitermination sequences. Transcription from the P1 promoter of rrn is unaffected by the absence of YbeY, but the transcription is almost abolished if the promoter region also contains the P2 and nut -like sequences which constitute the antitermination region. The presence of tL – the Rho-independent pause site in the promoter region which contains the transcriptional antitermination site elevated the level of transcription – compare the effect of the deletion on transcription from the “M” promoter and the “L” promoter. The tL is a conserved sequence in the leader region of rRNA and various deletions of the tL results in rRNA transcription polarity. It appears that tL may assist a correct transcription antitermination process, and its presence enables the complex to be fully organized and stabilized prior to the transcription of the 16S rRNA. The lack of tL may lead to premature termination during transcription. The effect of tL on transcription can be seen in Fig. 1, as its presence stimualtes transcription in the wild type bacteria. Interestingly, the effect of tL remains even in deletion mutants of ybeY where its presence increases the transcription level as well. Yet even in the presence of tL there is still a 50% decrease in transcription of rrn. Such a decrease is probably sufficient to cause the phenotypes seen in the ybeY deletion mutants, as its effect may escalate into the major effect on ribosome biogenesis. We assume that the reduced level of transcripts overlapping the transcriptional antitermination region in ybeY mutants results from the involvement of YbeY in the transcriptional antitermination process.