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pairs with G). The potato spindle tuber viroid and tomato plant macho viroid, both members of the family Pospiviroidae, replicate in the cell nucleus. A cellular enzyme, RNA polymerase, copies the circular RNA of the viroid to make a linear, repeated copy of the genome in complementary or "negative sense." This RNA is copied again to make another linear, repeated "positive sense" RNA. Cellular enzymes cut this second copy of RNA at each place where the genome begins a repetition, yielding multiple copies of the genome. These copies then reassume a circular shape to make new viroid RNA.

The members of the second family of viroids, the Avsunviroidae, replicate in cell chloroplasts. Two are known, the avocado sunblotch viroid and the peach latent mosaic viroid. In both of these species, RNA polymerase makes a long, linear negative sense RNA. This RNA contains a catalytic ribozyme sequence, which cleaves itself. The negative sense RNA resumes its customary circular shape and is copied to form linear positive sense RNA. The ribozyme again cleaves this RNA, yielding linear genomic units that again recircularize, forming viroids.

The differing replication strategies of these two groups reflect different evolutionary origins. Viroids move through the plant in the phloem and plasmodesmata, which are part of the plant's circulatory system. They propagate by mechanical means, vegetative reproduction, and possibly via seeds and insects. They cause plant diseases following interactions with proteins. For example, when they interact with an enzyme that impairs protein synthesis, the growth of the host plant may be stunted. This can have severe economic consequences.

complementary matching opposite, like hand and glove ribozyme RNA-based catalyst in a cell, excluding the nucleus

How To Can Tangy Tomatoes

How To Can Tangy Tomatoes

Interested In Canning Juicy Tomatoes? Here's How You Can Prepare Canned Tomatoes At Home. A Comprehensive Guide On Tomato Canning. The process of canning tomatoes at home has been a family tradition with many generations. Making home canned or home tinned tomatoes is something that is remembered by families for years! You must have surely seen your granny canning tomatoes at home in order to prepare for the approaching winters. In winters, one is usually unsure of getting fresh tomatoes.

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