Analytical observations (in silico) indicate molecular features of SARS-Cov2 genome that potentially explains the high prevalence of asymptomatic cases in Covid-19 pandemic. We observed that the virus maintains a low preference for ‘GGG’ codon for glycine (3%) in its genome. We also observed multiple putative introns of 26–44 nucleotide (nt) length in the genomic region between the coding regions of Nsp10 and RPol in the viral ORF1ab, like several other beta-coronaviruses of similar infectivity levels. It appears that the virus employs a dual strategy to ensure unhindered replication within the host. One of the strategies employ a (− )1 frameshift translation event through programmed ribosomal slippage at the ribosomal slippage site in the ORF1ab. The alternate strategy relies on intron excision to generate a read through frame. The presence of ‘GGG’ in this conserved ribosomal slippage site ensures adequate tRNA in cytoplasm to match the codon, implying no additional frameshift translation due to ribosomal stalling. With fewer replication events, viral load remains low and resulting in asymptomatic cases. We suggest that this strategy is the primary reason for the prevalence of asymptomatic cases in the disease, enabling the virus to spread rapidly.

分析观察（计算机）表明 SARS-Cov2 基因组的分子特征可能解释了 Covid-19 大流行中无症状病例的高流行。我们观察到该病毒在其基因组中对甘氨酸（3％）的“GGG”密码子保持较低的偏好。我们还在病毒 ORF1ab 中 Nsp10 和 RPol 编码区之间的基因组区域中观察到多个假定的 26-44 个核苷酸 (nt) 长度的内含子，就像其他几种具有相似感染性水平的 β 冠状病毒一样。该病毒似乎采用了双重策略来确保在宿主内不受阻碍地复制。其中一种策略通过ORF1ab中核糖体滑移位点处的程序化核糖体滑移采用 (−)1 移码翻译事件。另一种策略依赖于内含子切除来生成通读帧。这个保守的核糖体滑移位点中“GGG”的存在确保了细胞质中有足够的 tRNA 与密码子匹配，这意味着不会因核糖体停滞而产生额外的移码翻译。由于复制事件较少，病毒载量仍然较低，并导致无症状病例。我们认为，这种策略是该病无症状病例流行的主要原因，使病毒能够迅速传播。