title: Post-transcriptional regulation of ribosomal protein genes during serum starvation in Entamoeba histolytica.
abstract: Ribosome synthesis involves all three RNA polymerases which are co-ordinately regulated to produce equimolar amounts of rRNAs and ribosomal proteins (RPs). Unlike model organisms where transcription of rRNA and RP genes slows down during stress, in E. histolytica rDNA transcription continues but pre-rRNA processing slows down and unprocessed pre-rRNA accumulates during serum starvation. To investigate the regulation of RP genes under stress we measured transcription of six selected RP genes from the small- and large-ribosomal subunits (RPS6, RPS3, RPS19, RPL5, RPL26, RPL30) representing the early-, mid-, and late-stages of ribosomal assembly. Transcripts of these genes persisted in growth-stressed cells. Expression of luciferase reporter under the control of two RP genes (RPS19 and RPL30) was studied during serum starvation and upon serum replenishment. Although luciferase transcript levels remained unchanged during starvation, luciferase activity steadily declined to 7.8% and 15% of control cells, respectively. After serum replenishment the activity increased to normal levels, suggesting post-transcriptional regulation of these genes. Mutations in the sequence -2 to -9 upstream of AUG in the RPL30 gene resulted in the phenotype expected of post-transcriptional regulation. Transcription of luciferase reporter was unaffected in this mutant, and luciferase activity did not decline during serum starvation, showing that this sequence is required to repress translation of RPL30 mRNA, and mutations in this region relieve repression. Our data show that during serum starvation E. histolytica blocks ribosome biogenesis post-transcriptionally by inhibiting pre-rRNA processing on the one hand, and the translation of RP mRNAs on the other.
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: j.ahamadjnu@gmail.com.
authors.forename: Jamaluddin
authors.initials: J
authors.lastname: Ahamad
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: sandy.mbt@gmail.com.
authors.forename: Sandeep
authors.initials: S
authors.lastname: Ojha
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: ankita26@gmail.com.
authors.forename: Ankita
authors.initials: A
authors.lastname: Srivastava
authors.affiliation: School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: alok.bhattacharya@gmail.com.
authors.forename: Alok
authors.initials: A
authors.lastname: Bhattacharya
authors.affiliation: School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: sbjnu110@gmail.com.
authors.forename: Sudha
authors.initials: S
authors.lastname: Bhattacharya
mesh_terms: D019677:Artificial Gene Fusion; D016895:Culture Media, Serum-Free; D004748:Entamoeba histolytica / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D008156:Luciferases / Q000032:analysis / Q000235:genetics; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D038621:Regulatory Sequences, Ribonucleic Acid; D012269:Ribosomal Proteins / Q000096:biosynthesis*; D013312:Stress, Physiological
chemical_list: D016895:Culture Media, Serum-Free; D038621:Regulatory Sequences, Ribonucleic Acid; D012269:Ribosomal Proteins; D008156:Luciferases
keywords: 5′ Untranslated region (5′ UTR); Entamoeba histolytica; Post-transcriptional regulation; Pre-rRNA accumulation; Ribosomal proteins