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''Alphasatellites'' are single stranded satellite DNA that are dependent on a virus for transmission. The genome is a single circular single strand DNA molecule. The first alphasatellites were described in 1999 and were associated with cotton leaf curl disease and Ageratum yellow vein disease. As begomoviruses are being characterised at the molecular level an increasing number of alphasatellites are being described. These viruses were earlier known as DNA 1 components. These viruses are generally found in the Old World. A number have been isolated from the New World but their association with their host viruses is still being studied. ==Genome== The genome is between 1300 and 1400 nucleotides in length and has three conserved features: a hairpin structure, a single open reading frame (ORF) and an adenine rich region. The hairpin structure has a loop that includes the nonanucleotide, TAGTATTAC, which is common to nanoviruses and differs from the TAATATTAC sequence of geminiviruses by one nucleotide. In both geminiviruses and nanoviruses this sequence contains the origin of replication (''ori'') and is nicked by the rolling circle replication initiator protein to initiate viral DNA replication. On the basis of the hairpin structures alphasatellites can be divided into 5 clades. The open reading frame encodes a rolling circle replication initiator protein (Rep) similar to that found in the nanoviruses. The encoded protein is 32–37 kiloDalton in molecular weight with ~320 amino acids. It is highly conserved with 86.3–100.0% amino acid sequence identy between isolates. The adenine rich region is immediately downstream of the ''rep'' gene and is approximately 153–169 nucleotides in length with an adenine content of between 52.3–58.4%. Phylogenectic analysis of this region shows that they can be divided into three clades which correspond to those found on phylogenetic analysis of the entire genome.〔 This portion of the genome appears to be redundant. A putative second ORF in the genome of an alphasatellite virus has been described. The significance of this finding (if any) is not known. Recombination occurs between alphasatellites. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alphasatellite」の詳細全文を読む スポンサード リンク
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