Novel coding, translation, and gene expression of a replicating covalently closed circular RNA of 220 nt

AbouHaidar MG, Venkataraman S, Golshani A, Liu B, Ahmad T

Proc. Natl. Acad. Sci. U.S.A. 2014 Sep;

PMID: 25253891


The highly structured (64% GC) covalently closed circular (CCC) RNA (220 nt) of the virusoid associated with rice yellow mottle virus codes for a 16-kDa highly basic protein using novel modalities for coding, translation, and gene expression. This CCC RNA is the smallest among all known viroids and virusoids and the only one that codes proteins. Its sequence possesses an internal ribosome entry site and is directly translated through two (or three) completely overlapping ORFs (shifting to a new reading frame at the end of each round). The initiation and termination codons overlap UGAUGA (underline highlights the initiation codon AUG within the combined initiation-termination sequence). Termination codons can be ignored to obtain larger read-through proteins. This circular RNA with no noncoding sequences is a unique natural supercompact “nanogenome.”

Viral and chloroplastic signals essential for initiation and efficiency of translation in Agrobacterium tumefaciens

Ahmad T, Venkataraman S, Hefferon K, AbouHaidar MG

Biochem. Biophys. Res. Commun. 2014 Sep;452(1):14-20

PMID: 25117444


The construction of high-level protein expression vectors using the CaMV 35S promoter in concert with highly efficient translation initiation signals for Agrobacterium tumefaciens is a relatively less explored field compared to that of Escherichia coli. In the current study, we experimentally investigated the capacity of the CaMV 35S promoter to direct GFP gene expression in A. tumefaciens in the context of different viral and chloroplastic translation initiation signals. GFP expression and concomitant translational efficiency was monitored by confocal microscopy and Western blot analysis. Among all of the constructs, the highest level of translation was observed for the construct containing the phage T7 translation initiation region followed by the chloroplastic Rubisco Large Subunit (rbcL) 58-nucleotide 5′ leader region including its SD-like sequence (GGGAGGG). Replacing the SD-like (GGGAGGG) with non SD-like (TTTATTT) or replacing the remaining 52 nucleotides of rbcL with nonspecific sequence completely abolished translation. In addition, this 58 nucleotide region of rbcL serves as a translational enhancer in plants when located within the 5′ UTR of mRNA corresponding to GFP. Other constructs, including those containing sequences upstream of the coat proteins of Alfalfa Mosaic Virus, or the GAGG sequence of T4 phage or the chloroplastic atpI and/or PsbA 5′ UTR sequence, supported low levels of GFP expression or none at all. From these studies, we propose that we have created high expression vectors in A. tumefaciens and/or plants which contain the CaMV 35S promoter, followed by the translationally strong T7 SD plus RBS translation initiation region or the rbcL 58-nucleotide 5′ leader region upstream of the gene of interest.

Recent patents involving virus nucleotide sequences; host defense, RNA silencing and expression vector strategies

Ahmad T, AbouHaidar M, Hefferon KL

Recent Pat DNA Gene Seq 2011 Dec;5(3):202-13

PMID: 21867477


Improved knowledge of the molecular biology of viruses, including recent gains in virus sequence data analysis, has greatly contributed to recent innovations in medical diagnostics, therapeutics, drug development and other related areas. Virus sequences have been used for the development of vaccines and antiviral agents to block the spread of viral infections, as well as to target and battle chronic diseases such as cancer. Virus sequences are now routinely employed in a wide array of RNA silencing technologies. Viruses can also be engineered into expression vectors which in turn can be used as protein production platforms as well as delivery vehicles for gene therapies. This review article outlines a number of patents that have been recently issued with respect to virus sequence data and describes some of their biotechnological applications.