Disease relevance of RL1

• In the published DNA sequence of herpes simplex virus type 1 (HSV-1) strain 17 the coding region for the neurovirulence factor ICP34.5 is disrupted by a 2 bp insertion relative to the corresponding sequence in HSV-1 strain F; this difference would render 60% of the ICP34.5 coding sequence out of frame in strain 17 [1].
• Characterization of the herpes simplex virus type 1 strain 17+ neurovirulence gene RL1 and its expression in a bacterial system [2].
• Similarly to HSV-1, deletion of the region spanning RL1 abolishes the virulence of HSV-2 strain HG52 and its ability to grow in stationary 3T6 cells [3].
• All genes identified in SA8 are homologous and collinear with those of the monkey B virus, including the lack of the RL1 open reading frame, a gene responsible for neurovirulence in human herpes simplex viruses [4].
• The entire RL1 open reading frame was cloned into the expression vector pET8c to enable over-expression of ICP34.5 in Escherichia coli [2].

High impact information on RL1

• However, internalization is blocked completely when viruses lack the neurovirulence factor, infected cell protein 34.5, or when endocytosis is inhibited with bafilomycin A(1) or chloroquine [5].
• The HSV gene RL1 (gamma(1)34.5; neurovirulence factor) is not present in HVP-2, as is the case for SA8 and B virus [6].
• Herpes simplex virus type-1 (HSV1) in which the neurovirulence factor ICP34.5 is inactivated has been shown to direct tumour-specific cell lysis in several tumour models [7].
• It has previously been demonstrated that variants of HSV-1 which are deleted in the RL1 gene and fail to produce the virulence factor ICP34.5 are potential candidates for tumour therapy [8].
• ORF-P, the first and largest open reading frame (ORF) encoded by the L/STs, overlaps >90% of the ORF encoding ORF-34.5, a putative neurovirulence factor, which is transcribed from the opposite DNA strand [9].

Biological context of RL1

• Although an open reading frame (ORF) was predicted in HSV-1(F) and shown to encode a polypeptide called ICP34.5, only recently has a corresponding ORF, designated RL1, been recognized in HSV-1(17) [10].
• The second was mouse embryo testicular carcinoma F9 cells which, in the undifferentiated state, provide a reversal of phenotype; wild-type virus fails to grow but RL1-negative virus replicates efficiently [11].
• To determine whether the HSV-1(17) ORF is expressed, we raised antipeptide sera against predicted amino acid sequences from RL1; one serum specifically recognized a 37K protein in HSV-1(17)-infected cell extracts [10].
• 5. Hence RL1-negative mutants have the distinct advantage of providing a double hit phenomenon whereby cell death could occur by either pathway [12].
• L/ST-4BS was completely attenuated for neurovirulence (LD50 > 10(6) PFU) relative to wild-type virus (LD50 < 900 PFU), although the four single-base-pair substitutions lie outside the coding region for the neurovirulence factor, ICP34 [9].

Anatomical context of RL1

• Null mutants in RL1 fail to replicate in the central nervous system of mice and are therefore totally non-neurovirulent [11].
• The first was mouse embryo fibroblast 3T6 cells, in which RL1-negative mutants are impaired and the in vivo phenotype is mimicked [11].
• To this end, the lateral ventricle of nude mice was injected with high (2.5 x 10(7) PFU), medium (10(5) PFU), or low dose (10(3) PFU) HSV-1 variant-1716, which has a deletion in the RL-1 gene [13].

Analytical, diagnostic and therapeutic context of RL1

• The specificity of the anti-serum directed against the E. coli-expressed ICP34.5 was defined by Western blotting of wild-type and RL1-negative infected cell extracts [2].
• Sequence analysis predicts that herpes simplex virus type 2 (HSV-2) strain HG52 contains an open reading frame, RL1, encoding a polypeptide equivalent to ICP34.5 of HSV-1 [3].
• The herpes simplex virus type 1 (HSV-1) RL1 deletion mutant 1716 has properties that make it a promising candidate as a viral vector for gene therapy in the human nervous system [14].

References