Reverse transcriptases catalyze three different reactions: (1) RNAdependent DNA synthesis, (2) RNA degradation, and (3) DNA-dependent DNA synthesis. Like many DNA and RNA polymerases, reverse transcriptases contain Zn 2+ .

Each transcriptase is most active with the RNA of its own virus, but each can be used experimentally to make DNA complementary to a variety of RNAs. The DNA and RNA synthesis and RNA degradation activities use separate active sites on the protein. For DNA synthesis to begin, the reverse transcriptase requires a primer, a cellular tRNA obtained during an earlier infection and carried in the viral particle.

This tRNA is base-paired at its 3′ end with a complementary sequence in the viral RN The new DNA strand is synthesized in the 5′ → 3′ direction, as in all RNA and DNA polymerase reactions. Reverse transcriptases, like RNA polymerases, do not have 3′ → 5′ proofreading exonucleases.

They generally have error rates of about 1 per 20,000 nucleotides added. An error rate this high is extremely unusual in DNA replication and seems to be a characteristic of most enzymes that replicate the genomes of RNA viruses. A consequence is a higher mutation rate and faster rate of viral evolution, which is a factor in the frequent appearance of new strains of disease-causing retroviruses.

水刷石

斩假石

花岗石

玻化砖

正确

错误

石材墙面

碎拼石材墙面

装饰板墙面

块料墙面

塑料板面层所用的塑料板块卷材的品种、规格、颜色、等级应符合设计要求和现行国家标准的规定

板块的焊接，焊缝应平整、光洁，无焦化变色、斑点、焊瘤和起鳞等缺陷，其凹凸允许偏差为±0.6mm。焊缝的抗拉强度不得小于塑料板强度的75%

塑料板面层应表面洁净，图案清晰，色泽一致，接缝严密、美观。拼缝处的图案、花纹吻合，无胶痕；与墙边交接严密，阴阳角收边方正

镶边用料应尺寸准确、边角整齐、拼缝严密、接缝顺直

面层与下一层的粘接应牢固，不翘边、不脱胶、无溢胶

砂浆制作、运输

砌砖、砌块

石表面加工

勾缝、材料运输

涂料

壁纸

人造装饰板

以上都是

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向右侧转身成右前侧丁字步，左手下格挡。

向左侧转身成左前侧丁字步，右手下格挡。

向左侧转身成左前侧弓步，左手下格挡。

Reverse auction is most often found in B2B whereas mass customization is often found in B2C.

Reverse auction requires a bid from consumers whereas mass customization requires a bid from suppliers.

Mass customization require a click-and-mortar environment; reverse auctions do not.

Mass customization can sell digital products; reverse auctions sell commoditylike products.