Abstract
The amoeba Dictyostelium discoideum is a well established model organism for studying numerous aspects of cellular and developmental functions. Its ribosomal RNA (rRNA) is encoded in an extrachromosomal palindrome that exists in ∼100 copies in the cell. In this study, we have set out to investigate the sequence of the expressed rRNA. For this, we have ligated the rRNA ends and performed RT-PCR on these circular RNAs. Sequencing revealed that the mature 26 S, 17 S, 5.8 S, and 5 S rRNAs have sizes of 3741, 1871, 162, and 112 nucleotides, respectively. Unlike the published data, all mature rRNAs of the same type uniformly display the same start and end nucleotides in the analyzed AX2 strain. We show the existence of a short lived primary transcript covering the rRNA transcription unit of 17 S, 5.8 S, and 26 S rRNA. Northern blots and RT-PCR reveal that from this primary transcript two precursor molecules of the 17 S and two precursors of the 26 S rRNA are generated. We have also determined the sequences of these precursor molecules, and based on these data, we propose a model for the maturation of the rRNAs in Dictyostelium discoideum that we compare with the processing of the rRNA transcription unit of Saccharomyces cerevisiae.
Highlights
Ribosomes belong to the most important molecular machines in the cell
We have determined the sequences of these precursor molecules, and based on these data, we propose a model for the maturation of the ribosomal RNA (rRNA) in Dictyostelium discoideum that we compare with the processing of the rRNA transcription unit of Saccharomyces cerevisiae
There, two transcripts for each rRNA are annotated that show variable sequences and ends, with the exception of the 5 S rRNA. These entries were generated by an automated gene prediction from the available sequences of the D. discoideum rRNA palindrome encoding the rRNAs [7], because their sizes do not coincide with the actual migration
Summary
This solution is implemented for the amoeba Dictyostelium discoideum [5, 6]; here, the rDNA clusters are localized on extrachromosomal elements, rather than within the chromosomes These show a size of 88 kb with a palindromic organization of two rRNA transcription units on the mirror-symmetric arms [7, 8]. The genes for the 5 S rRNA and the other rRNAs are frequently unlinked (Ref. 14 and references therein), they are still connected in the palindrome of Dictyostelium [5], similar to the situation in yeast [15] Despite this physical association, there are two transcription start sites, in the amoeba [14]. We propose a scheme for the processing of the primary transcript to yield mature rRNA
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
